early 15c., "to make similar or the same; to balance or harmonize; distribute (ingredients) uniformly; reduce to evenness or smoothness; to set (a fracture)," from Latin aequatus "level, levelled, even, side-by-side," past participle of aequare "make even or uniform, make equal," from aequus "level, even, equal" (see equal, adj.). Earliest use in English was of astrological calculation, then "to make equal;" meaning "to regard as equal" is early 19c. Related: Equated; equating.