c. 1300, mounten, "to get up on a horse;" mid-14c., "to rise up, rise in amount, ascend; fly," from Old French monter "to go up, ascend, climb, mount," from Vulgar Latin *montare, from Latin mons (genitive montis) "mountain" (from PIE root *men- (2) "to project"). The transitive meaning "to set or place in position" first recorded 1530s. Sense of "to get up on for purposes of copulation" is from 1590s. Meaning "prepare for presentation or exhibition" is by 1712. Military meaning "set up or post for defense" is by 1706; to mount an attack is by 1943. Related: Mounted; mounting.
"mountain, lofty hill, elevation of land," late Old English, from Anglo-French mount, Old French mont "mountain;" also perhaps partly from Old English munt "mountain;" both the Old English and the French words from Latin montem (nominative mons) "mountain," from PIE root *men- (2) "to stand out, project." "From the 17th c. in prose used chiefly of a more or less conical hill of moderate height rising from a plain; a hillock" [OED]. Archaic or poetic only by late 19c. except as part of a proper name.
late 15c., "an act of mounting," from mount (v.) or from Old French monte. Sense of "that on which something is fixed for use and by which it is supported and held in place" is by 1739. The colloquial meaning "a horse for riding" is recorded by 1831 in sporting magazines.