Imperfect
Middle English imparfit, imperfet, from Old French imparfait, from Latin imperfectus, from in- ‘not’ + perfectus (see perfect). The spelling change in the 16th century was due to association with the Latin form.
wiktionary
From Middle English imperfit, from Old French imparfit (modern French imparfait), from Latin imperfectus. Spelling modified 15c. to conform Latin etymology. See im- + perfect.
etymonline
imperfect (adj.)
late 14c., imparfit, "sinful, immoral; not properly formed, not complete, immature; rudimentary, elementary," from Old French imparfait, from Latin imperfectus "unfinished, incomplete, immature," from assimilated form of in- "not, opposite of" (see in- (1)) + perfectus "finished, complete" (see perfect (adj.)). Altered mid-16c. to conform to Latin, along with perfect. Related: Imperfectly.
