argumentum

Argumentum, argumenti is second declension neuter, from arguo, "I make clear, prove", so the root sense is the evidence that makes a case clear rather than the quarrel English often means by "argument". Latin never uses it for a row. For that you want rixa, iurgium or altercatio.

The second sense catches people out. The argumentum of a play, a poem or a book is its plot or subject matter, and manuscripts print an argumentum at the head of a work as a summary. Scholastic Latin then produced the tags that survive in English: argumentum ad hominem, argumentum e silentio. Note the neuter plural argumenta looks feminine singular, so argumenta vera sunt takes a plural verb.