if

if O.E. gif (initial g- in O.E. pronounced with a sound close to Modern English -y-), from P.Gmc. *ja-ba (Cf. O.S., O.N. ef, O.Fris. gef, O.H.G. ibu, Ger. ob, Du. of "if, whether"), from PIE pronomial stem *i- [Watkins]; Klein, OED suggest probably originally from an oblique case of a noun meaning "doubt" (Cf. O.H.G. iba "condition, stipulation, doubt," O.N. if "doubt, hesitation," Swed. jäf "exception, challenge"). As a noun from 1510s.