What's the "een" in Halloween?
late 14c., "outcome of an action," from Old French esploit (12c.), a very common word, used in senses of "action, deed, profit, achievement," from Latin explicitum "a thing settled, ended, displayed," neuter of explicitus, past participle of explicare "unfold" (see explicit).
Meaning "feat, achievement" is c.1400. Sense evolution is from "unfolding" to "bringing out" to "having advantage" to "achievement." Related: Exploits.
c.1400 espleiten, esploiten "to accomplish, achieve, fulfill," from Old French esploitier, espleiter, from esploit (see exploit (n.)).
The sense of "use selfishly" first recorded 1838, from French, perhaps extended from use of the word with reference to mines, etc. (cf. exploitation). Related: Exploited; exploiting. As an adjective form, exploitative (1882) is from French; exploitive (by 1859) appears to be a native formation.