plus

Plus is the comparative of multus, and it is really two words wearing one entry. In the SINGULAR it is a neuter NOUN, not an adjective, so whatever it measures goes into the genitive: plus vini is "more wine", literally "more of wine", and plus pecuniae is "more money". In the PLURAL it turns into a genuine third declension adjective, plures for masculine and feminine, plura for neuter, genitive plurium, and it agrees with its noun in the ordinary way: plures homines, plura verba.

As a bare adverb with a verb it means "more" and needs no case at all: plus dixit.

Comparison is by quam or by the ablative of comparison, and with numbers Latin often drops the quam altogether, so plus mille homines is perfectly good for "more than a thousand men". The superlative is plurimus, "very many, most". English took plus, plural, plurality and surplus, and French plus and Italian piu are the word itself. Spanish and Portuguese went the other way and built their "more" out of magis instead, giving mas and mais.