Apart

google

ref

late Middle English: from Old French, from Latin a parte ‘at the side’.

wiktionary

ref

From Middle English apart, aparte, a-part, a part, from Anglo-Norman a part, from Latin ad partem(“to the side”).

etymonline

ref

apart (adv.)

"to or at the side; by itself, away from others," late 14c., from Old French a part (Modern French à part) "to the side," from Latin ad "to" (see ad-) + partem, accusative of pars "a part, piece, a faction, a part of the body" (from PIE root *pere- (2) "to grant, allot"). The first element is probably felt in English as a- as in abroad, ahead (see a- (1)). As an adjective from 1786.