1560s, "to fight, struggle, contend" (intransitive), from French combat (16c.), from Old French combattre (12c.), from Late Latin combattere, from Latin com "with (each other)," see com-, + battuere "to beat, fight" (see batter (v.)). Transitive sense is from 1580s; figurative sense from 1620s. Related: Combated; combating; combatted; combatting.
word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).
<a href="https://www.etymonline.com/word/combative">Etymology of combative by etymonline</a>
Harper, D. (n.d.). Etymology of combative. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/combative