When were different agent noun endings used in Ancient Greek?

Question

In Ancient Greek, it seems that there were various endings for agent nouns. Thomas Dwight Goodell's School Grammar of Attic Greek (1902) mentions -τηρ, -τωρ, -της, -εύς, -τειρα, -τρια, -τρις (-τριδ-), -τις (-τιδ-) (§405).

Goodell says that the first four are masculine, and the last four are feminine, but the table of examples in that section includes two -τωρ nouns that cross over between the masculine and feminine categories: ῥήτωρ "speaker" and ἵστωρ "one who knοws" (Goodell's definitions). I assume this means that these are what is called "common gender" nouns: grammatically feminine when they refer to a female person, and grammatically masculine when they refer to a male person. In contrast, συλλήπτωρ "helper" is shown as an exclusively masculine noun with a feminine counterpart συλλήπτρια.

Is this description accurate? If so, how frequent is each type of agent noun? Are there any ways to predict which ending(s) an agent noun will take, and whether an agent noun ending in -τωρ will be common gender or (exclusively?) masculine?

Answer 1

Here is some information that I have found since posting the question.

the -τηρ and -τωρ suffixes were not productive in forming agent nouns in Greek. Already in Ionic-Attic Greek, the agent noun suffix -της was being substituted for -τηρ, and by the time of Hellenistic Greek, the -της suffix became the predominant suffix for agent nouns.⁵ In fact, -της had so overtaken -τηρ as an agent noun suffix that Palmer claims that “-τηρ agent nouns survived as words with an archaic flavour in the vocabulary of law and religion [e.g. σωτήρ from σῴζω]. The insertion of -τηρ for -της was a self-conscious device of high stylization.”⁶ (2) More commonly in Hellenistic Greek, the -τηρ suffix designated numerous words for tools and instruments, [...]

⁵Moulton and Howard, Grammar, Vol. II, 365 §150. Statistically, Palmer recognizes the predominance of -της in the Post-Ptolemaic papyri, finding 421 words with the -της suffix, while finding 25 with the -τηρ suffix and 24 with the -τωρ suffix. See Leonard R. Palmer, A Grammar of the Post-Ptolemaic Papyri, Volume I: Accidence and Word-Formation (Oxford: Oxford University Press, 1945), 6-8. This can also be seen in the NT and early Christian literature, where Bauer’s Greek-English Lexicon , 3^rd ed. lists 216 words with the -της suffix, in contrast to 11 words with the -τηρ suffix and 15 words with the -τωρ suffix. Tribulato attempts to explain why the -της suffix dominated; see Olga Tribulato, Ancient Greek Verb-Initial Compounds: Their Diachronic Development Within the Greek Compound System (Berlin: Walter de Gruyter, 2015), 93-97.

⁶Palmer, The Greek Language, 254.

("The -τηριον Suffix: Its Origin and Development, Morphology, and Semantics", by Nelson S. Hsieh, 2016)