opponent (n.)

word-forming element meaning "toward; against; before; near; across; down," also used as an intensive, from Latin ob (prep.) "in the direction of, in front of, before; toward, to, at, upon, about; in the way of; with regard to, because of," from PIE root *epi, also *opi "near, against" (see epi-).

late 14c., posicioun, as a term in logic and philosophy, "statement of belief, the laying down of a proposition or thesis," from Old French posicion "position, supposition" (Modern French position) and directly from Latin positionem (nominative positio) "act or fact of placing, situation, position, affirmation," noun of state from past-participle stem of ponere "put, place." Watkins tentatively identifies this as from PIE *po-s(i)nere, from *apo- "off, away" (see apo-) + *sinere "to leave, let" (see site). But de Vaan identifies it as from Proto-Italic *posine-, from PIE *tkine- "to build, live," from root *tkei- "to settle, dwell, be home" (see home (n.)).

The meaning "place occupied by a person or thing" especially a proper or appropriate place, is from 1540s; hence "status, standing, social rank" (1832); "official station, employment" (1890). The meaning "manner in which some physical thing is arranged or posed, aggregate of the spatial relations of a body or figure to other such bodies or figures" is recorded by 1703; specifically in reference to dance steps, 1778, to sexual intercourse, 1883. Military sense of "place occupied or to be occupied" is by 1781.

late 14c., opposen, "to speak or act against; accuse, question, interrogate," from Old French oposer "oppose, resist, rival; contradict, state opposing point of view" (12c.), apparently from assimilated form of Latin ob- "in the direction of, in front of" (see ob-) + French poser "to place, lay down" (see pose (v.1)), with the sense blended with that of Latin opponere "oppose, object to, set against" (see opponent). The meaning "to set or place over against or directly opposite" (transitive) and "interpose effort or objection, be adverse, act adversely" (intransitive) are from 1590s. Related: Opposed; opposing.