Accomplice
mid 16th century: alteration (probably by association with accompany) of Middle English complice ‘an associate’, via Old French from late Latin complex, complic- ‘allied’, from com- ‘together’ + the root of plicare ‘to fold’.
wiktionary
First attested in the 1580s. From Middle English accomplice, from a complice, from Old French complice(“confederate”), from Latin complicare(“fold together”). The article a became part of the word, through the influence of the word accomplish.
etymonline
accomplice (n.)
"associate in crime," 1580s, an unetymological extension of earlier complice "an associate or confederate" (early 15c.), from Old French complice "a confederate, partner" (not in a criminal sense), from Late Latin complicem (nominative complex) "partner, confederate," from Latin complicare "to involve," literally "fold together," from com "with, together" (see com-) + plicare "to fold, weave" (from PIE root *plek- "to plait"). Altered perhaps on model of accomplish, etc., or by assimilation of the indefinite article in a complice.
