vir

Vir, viri is second declension masculine, but it drops the -us in the nominative and leaves a bare consonant, the same way puer, ager and liber do. The genitive viri tells you the rest of the pattern is entirely regular: virum, viro, viri, virorum, viris.

It means an adult MALE, and where the context is marriage it means a husband, with uxor as its partner. The distinction from homo is the one to fix, because English "man" flattens it: homo is a human being of either sex, vir is a man. Every vir is a homo; not every homo is a vir. When a Roman writer chooses vir he is usually making a point about manhood, standing or courage rather than just identifying somebody.

That is why the abstract noun built on it, virtus, starts as "manliness", widens to courage, and ends as the whole moral idea English calls virtue. The compounds triumvir, decemvir and duumvir name the boards of men who held Roman offices. Vir is also a straight cognate of the -wer in "werewolf", which is a man-wolf and not a wolf that wears anything.