General question about nouns and adjectives (can nouns be adjectives and how to decline)

Question

I know that in Latin, adjectives can act as nouns (substantives) e.g.

Romani urbem petiverunt.
The Romans attacked the city.

However, can nouns act as adjectives? For example, stone (lapis, m) and table (mensa, f) are both nouns. But if I wanted to say stone stable... is stone here an adjective? If so, does it become feminine?

I presume they both decline as usual (e.g. ablative singular would be lapide mensa).

If I wanted to say "big stone table", would "big" agree with "table" (the main "noun" i.e. magna lapide mensa) or "stone" (proximity rule, magno lapide mensa)?

Answer 1

In English you can just put two nouns next to each other and say "stone table", but in Latin you cannot. There are a couple of ways to go about this in Latin:

1. Use an adjective derived from the noun. The one for lapis is lapideus, "made from stone". A stone table can be called mensa lapidea.

   To do this you have to know or create the corresponding adjective. Latin is quite productive with these derivatives, so I wouldn't be opposed to coining a new adjective if in need. The typical suffix for this is -eus, but in most cases there is a pre-existing adjective you should use. If you want to say "a wood table" in Latin, the word you need to look up is not "wood" but "wooden".

2. Tell what the object was made of. Just like you can say "a table made of stone" in English, you can say mensa e lapide facta in Latin.

   This has the benefit of not having to derive an adjective. The prepositional phrase e lapide or ex marmore or whatever stays put, and only the pair mensa facta declines to the required case and number.

   I chose the generic factus, "made". In some cases you may prefer a more precise verb, like "carved".

3. Use the genitive of material. The English "a table of stone" has the Latin counterpart mensa lapidis.

   This is simplest to use as it requires no other words (no derived adjective, no participle of a verb). The genitive stays as it is as the main word is declined to whatever form it needs to be in.

   For some reason this feels a bit less natural to me than the other two options, but it might well be a matter of personal preference rather than actual grammar.

If your stone table is big, you can add an additional adjective: magna mensa lapidea or magna mensa e lapide facta or magna mensa lapidis.

Interestingly, the gender of the material (lapis being masculine) has no effect on the use. In the first option the derived adjective needs to be put in the right gender and in the second and third ones the gender doesn't appear in any way.

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See also this older question on noun adjuncts in Latin. The answers there will give a broader view of the matter.