An Etymological Dictionary of Astronomy and Astrophysics

(Conjunction) in case that; granting or supposing that; on condition that. → if and only if.

Etymology (EN): M.E., from O.E. gif; akin to O.H.G. ibu “if.”

Etymology (PE): Agar “if,” from Mid.Pers. agar, hakar “if;” O.Pers. ha-karam “once;” from ha- “one,” variant ham-, → com- (cf. Av. ha-; Skt. sa-; Gk. ha-; L. sem-; PIE *sem- “one”), + karam- “a time,” maybe from kar- “to do; doing,” → work; cf.
Av. hakərət “once;” Skt. sakrt “once;” Gk. hapaks “once;” L. semel “once.”