1530s, "full of foam," from froth + -y (2). Meaning "vain, light, insubstantial" is from 1590s. Related: Frothiness.
Entries linking to frothy
froth n.
c. 1300, from an unrecorded Old English word, or else from Old Norse froða "froth," from Proto-Germanic *freuth- "froth" (source also of Swedish fradga, Danish fraade). Old English had afreoðan "to froth," from the same root. The modern verb is late 14c., from the noun. Related: Frothed; frothing.
-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.