mid-13c., "theft, action or practice of stealing," from O.E. *stælþ, which is related to stelen (see steal), from P.Gmc. *stælitho (cf. O.N. stulþr). Sense of "secret action" developed c.1300, but the word also retained its etymological sense into 18c. Got a boost as an adj. from stealth fighter, stealth bomber, radar-evading U.S. military aircraft, activated 1983.