- (archaic) Contraction of .
Of uncertain origin. The spelling ef'n is attested since at least 1909. Perhaps a compound of if and an (“if”) (a variant, attested since Middle English, of and (“if”); compare an if and gin (“if”)); if an is attested since at least the 1700s. Alternatively, perhaps a compound of if and -in', generalized from conjunctional uses of considering, excepting, and so on, or of if and -en as in offen (“off”), outen (“out”) (which goes back to Old English ūtan), etc. Compare less'n.
- “iffen” in Dictionary.com Unabridged, Dictionary.com, LLC, 1995–present.
- Grammarphobia: iffen, which also says the Dictionary of American Regional English speculates that if and is the origin
- Paul Dickerson Brandes, Jeutonne Brewer, Dialect clash in America: issues and answers (1977), page 296: The en suffix also appears in words other than verbs, e.g., outen in "Git outen thishere house"[,] offen in "I done bought it offen him fer tin cints"; and iffen in "Iffen you'uz to tell me he'uz daid, I wou'nt believe ye."