late 14c., "eager, assiduous; attentive, paying attention," from Old French ententif, intentif "attentive, solicitous, assiduous" (12c.), from Late Latin intentivus, from intent-, past-participle stem of Latin intendere "turn one's attention" (see intend). Related: Intentively; intentiveness.
"good faith, fair dealing, freedom from intent to deceive," by 1838, English pluralization of bona fide, as though the Latin phrase were a noun. Sense of "guarantees of good faith" is by 1944. The opposite is mala fides "bad faith, intent to deceive."
early 15c., "one who imitates or makes a copy of," especially with intent to deceive or defraud, agent noun from counterfeit (v.).