stealthy (adj.)

mid-13c., "theft, action or practice of stealing," from a probable Old English *stælþ, which is related to stelen (see steal (v.)), from Proto-Germanic *stælitho (source also of Old Norse stulþr), with Proto-Germanic abstract noun suffix *-itho (see -th (2)).

Compare heal/health, weal/wealth. Sense of "secret action" developed c. 1300, but the word also retained its etymological sense into 18c. Got a boost as an adjective from stealth fighter, stealth bomber, radar-evading U.S. military aircraft, activated 1983.

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.