c. 1400, "regard or treat as equal;" early 15c. "liken, make a comparison, represent as similar," from Old French comparer "to compare, liken" (12c.), from Latin comparare "to liken, to compare," from com "with, together" (see com-) + par "equal" (see par (n.)). Related: Compared; comparing.
From c. 1500 as "note the similarities and differences of." Intransitive sense "bear comparison" is from mid-15c. To compare notes is from 1708.
In phrase without compare (1620s, with similar phrasing to 1530s) it might be altered by folk etymology from compeer "rival" (with-outen compere is attested from c. 1400) or blended with it; Middle English had withouten comparacioun (mid-15c.), wyþe-oute comparisoun (mid-14c.).