1937, American English, from if + -y (2). Originally associated with President Franklin D. Roosevelt.
Entries linking to iffy
if conj.
"in case that; granting, allowing, or supposing that; on condition that;" also "although, notwithstanding that," Old English gif (initial g- in Old English pronounced with a sound close to Modern English -y-) "if, whether, so," from Proto-Germanic *ja-ba (source also of Old Saxon, Old Norse ef, Old Frisian gef, Old High German ibu, German ob, Dutch of "if, whether"), of uncertain origin or relation. Perhaps from PIE pronominal stem *i- [Watkins]; but Klein, OED suggest it probably originally from an oblique case of a noun meaning "doubt" (compare Old High German iba "condition, stipulation, doubt," Old Norse if "doubt, hesitation," Swedish jäf "exception, challenge"). As a noun from 1510s.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.