The word domus is normally a feminine, IVth declension noun and hence the adjectives that modify it are feminine.

However, sometimes domus appears to take masculine forms in some cases. For example, we have the "Comes Domorum" (the count of the houses), who was the official in charge of the imperial palaces. Likewise, the ablative domo and plural accusative domos are also found. What is the explanation for this? Why would domus have these gender-irregular forms?

4 Answers 4


In Old Latin domus (then domos) was usually declined as a second-declension noun, though it was feminine even then. It's probably the case that it was shifted into the fourth declension in an attempt to make its unusual gender make sense—so it's not the retained second-declension forms that are unusual, it's the new fourth-declension ones.
This actually happened to a greater or lesser extent for a lot of feminine second-declension nouns: e.g. nurus 'daughter-in-law' has fully joined the fourth declension (cf. its Greek cognate νυός, still a second-declension feminine), while fagus 'beech' and laurus 'laurel' are still in the second declension but also have an attested acc. pl. in -us. Feminine second-declension nouns seem to have confused Romans nearly as much as they confuse students today. (Conversely, quercus 'oak' is a native fourth-declension noun that has an attested gen. pl. quercorum.)
For domus, this shift was already underway in Old Latin, and pretty much completed in Classical Latin, apart from the occasional now-irregular form and archaism.

As for why domos was feminine in the first place, that's less clear. We can reconstruct perhaps three basic Proto-Indo-European words built on the root *dem- in the o-grade meaning 'house' based on reflexes in daughter languages:

  • Athematic root noun *dṓm < *dóm-s: Greek δῶ (neuter), Armenian town (no gender), Sanskrit dám (masculine)
  • Thematic (o-stem) *dóm-o-s: Greek δόμος (masculine), Sanskrit dáma (masculine)
  • Athematic u-stem *dóm-u-s: Old Church Slavonic domŭ (masculine), Lithuanian nãmas (masculine), Vedic Sanskrit dámūnas- (a derived adjective, 'of the house'), Armenian tanow-tēr (a compound, 'house-lord')

PIE o-stems gave rise to Latin's second declension and u-stems to its fourth, but as domus's membership of the fourth declension seems to be an innovation we can disregard influence from PIE *dómus (which is certainly masculine anyway). PIE o-stems in *-os were overwhelmingly masculine, and the Greek and Sankrit seem to confirm *dómos was too; by rights a Latin domus inherited from PIE *dómos should be masculine.

The gender of PIE athematics is less predictable (much like the Latin third declension, into which most of them went), and it's very inconvenient none of the high-profile reflexes of *dṓm is feminine. Mainly on the strength of Latin (!), *dṓm is still usually taken to be feminine, though, and if that's assumed, then Latin domus could have retained its feminine gender from it, after it either merged with *dómos or (in my view more likely) independently became thematised (in which case it effectively hopped declensions from the third to the second to the fourth over the centuries).

Some sources worth your time (though they don't say anything else that's relevant here, I don't think):

  • Michael Weiss, Outline of the Historical and Comparative Grammar of Latin.
  • Andrew L. Sihler, New Comparative Grammar of Greek and Latin.
  • Michiel De Vaan, Etymological Dictionary of Latin and the other Italic Languages.
  • 1
    One quibble: the Armenian cognate is (orthographic) town, (phonological) /tun/. I note that you use the orthographic spelling in tanow-. Otherwise an excellent answer,
    – fdb
    Commented Aug 10, 2021 at 10:10
  • @fdb Yeah, I got tanow- from Weiss and tun from Wiktionary, where it's positioned as if it's a transliteration, but I see it can't actually correspond to the word in the Armenian alphabet. Armenian isn't my area, obviously.
    – Cairnarvon
    Commented Aug 10, 2021 at 13:26

Genitive plural domōrum, ablative singular domō, and accusative plural domōs aren't masculine forms, they're second-declension forms.

It's true that most first-declension nouns are feminine and most second-declension nouns are masculine or neuter, but this is just a rule of thumb. Declension isn't necessarily linked to gender: nauta "sailor" is masculine, and quercus "oak" is feminine, for example. So a good sailor is a nauta bonus, and a good oak is a quercus bona, and good houses in the genitive plural are domōrum bonārum.


Although domus may look masculine, it's a feminine noun through and through — that is, there are no masculine forms, as you say.

According to Latin Grammar by Allen and Greenough:

90. Most nouns of the 4th Declension in -us are masculine.


The following are feminine:

acus, anus, colus, domus, īdūs (plural), manus, nurus, porticus, quīnquātrūs (plural), socrus, tribus

with a few names of plants and trees. Also, rarely, penus, specus.

From the Latin Grammar:

Grammatical Gender is a formal distinction as to sex where no actual sex exists in the object. It is shown by the form of the adjective joined with the noun.

In other words, gender is not tied to the declension or how the declension might appear to you, but to the adjectives joined with it.

Therefore, in spite of appearances, domus is feminine:

Case Singular Plural
Nominative domus domus
Genitive domus/domi domorum/domuum
Dative domui/domo/domu domibus
Accusative domum domus/domos
Ablative domu/domo domibus
Vocative domus domus
Locative domi domibus

In your example, Comes Domorum, there is no adjective involved — just the noun itself Domorum which is feminine. The same is true of domo, domos — all are feminine.

  • 2
    Uh, domorum is not femine. That is the masculine form. The feminine IVth declension genitive plural is domuum. I know that domus is feminine. I said that IN THE QUESTION ITSELF. There is no need to be telling me that domus is feminine. I KNOW THAT. The question is why does this feminine word have masculine forms. Commented Aug 9, 2021 at 11:35
  • 11
    @TylerDurden Those forms are not masculine or feminine in themselves. Most words in the second and fourth declensions are masculine, but the forms of those words are not called masculine forms. The term "masculine form" is only used for adjectives, where gender works with far fewer exceptions than in nouns. I fully agree with the answer: Those forms can look masculine by association to a lot of masculine nouns, but they are not masculine forms.
    – Joonas Ilmavirta
    Commented Aug 9, 2021 at 11:44
  • 1
    @JoonasIlmavirta I guess we are getting into semantics here, but I view -arum and -uum as feminine forms of the genitive and -orum as the masculine/neuter form of the plural genitive, and I think the Romans would agree with me. If a Roman overheard somebody talking and heard nothing but -orum, the Roman would assume men (or something masculine) was being discussed. Commented Aug 9, 2021 at 11:59
  • 8
    @TylerDurden I don't think that's correct. Neuter nouns also populate the second declension, and -orum is just as likely to be neuter plural as masculine plural. There's also a long list of islands and trees that are feminine second declension, the ending of which in genitive plural would be -orum while their modifying adjectives would end in -arum. That said, there is a question here why domus has two forms. I think the mix-up here just comes from different terminology used (i.e. to have said 2nd/4th decl. forms instead of m/f).
    – cmw
    Commented Aug 9, 2021 at 12:18
  • 4
    @TylerDurden Quin per silvam aliquam ambulas odoribusque suavibus altarum populorum, fagorum, fraxinorum, pinorum, alnorum, ulmorum delectaris? 😉 Commented Aug 9, 2021 at 17:09

We don't exactly know why domus has both second and fourth declension forms, but one possibility is that there were originally two separate words that merged, perhaps because a feminine second declension domus is unusual. It's also possible that there was only the o-stem and over time Romans used fourth declension endings for it, for the same reason as above.

From De Vaan:

In PIE, there was a root noun nom.sg. *dōm, gen. *dem-s. Probably, a u-stem derivative also existed (yielding Slav. *domu- 'house' and Gk. δμώς 'slave' < **dm-ou-).
The f. gender of domus probably is due to the original root noun. Old Latin mainly has o-stem forms; the change into a u-stem which some case forms show may be explained from an attempt to adapt the declension type of domus to its f. gender, which is unusual for Latin o-stems (apart from tree-names).

  • 1
    de Vaan does not say that these "were originally two separate words" that "merged". He says that this is one word, which shifted (at least partially) from 2nd to 4th declension.
    – fdb
    Commented Aug 10, 2021 at 8:19
  • 2
    @fdb I didn't say De Vaan said that. I said it. But De Vaan notes right there in the quoted text that "a u-stem derivative also existed." It ultimately doesn't matter whether the u-stem existed in Latin or was just created as a part of regularization, as either way we originally have an o-stem noun that shifted into a u-stem noun, and the most likely reason is that feminine 2nd declension nouns are a rarity. But you're right De Vaan doesn't actually say the u-stem derivative is also found in Latin or that they merged.
    – cmw
    Commented Aug 10, 2021 at 12:14
  • I'm confused by the reference to δμώς. Isn't it from a different PIE root, demh-, cognate with "tame?"
    – user3597
    Commented Aug 13, 2021 at 13:58
  • @BenCrowell It's the same root.
    – cmw
    Commented Aug 13, 2021 at 18:25

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