Is it ensure, insure, or assure?
1670s, "a false show, a pretended blow," from French feinte "a feint, sham," abstract noun from Old French feint (13c.) "false, deceitful," originally fem. past participle of feindre (see feign).
Borrowed late 13c. as adjective, but now obsolete in that sense. Also as a noun in Middle English with sense "false-heartedness" (early 14c.), also "bodily weakness" (c.1400).
c.1300, feinten, "to deceive, pretend," also "become feeble or exhausted; to lack spirit or courage," from feint (adj.); see feint (n.). Cf. Old French feintir "be slow, delay." Sense of "to make a sham attack" is first attested 1833. Related: Feinted; feinting.