"to put, place," mid-15c., reposen, "to put (something) back;" perhaps from re- "back, again" + pose (v.) or so formed in Middle English from Old French poser, on model of disposen "dispose" [Klein], or else from Latin repos-, infinitive stem of reponere "put back, set back, replace, restore; put away, lay out, stretch out," from re- + ponere "to put, place" (past participle positus; see position (n.)). Related: Reposed; reposing.
c. 1500, "act or state of rest from activity, temporary inaction, sleep," from Old French repos (11c.), a back-formation from reposer (see repose (v.1)). Meaning "state of quiet, freedom from disturbing influences" is by 1650s. As a noun, 17c. also used reposal, reposance.