late 14c., "of the air, made of air," from air, n.1 + -y(2). Meaning "breezy" is attested from 1590s; that of "lively" is from 1640s. Sense of "vain, unsubstantial" is from 1580s. Disparaging airy-fairy is attested from 1920 (earlier in a sense of "delicate or light as a fairy," which is how Tennyson used it in 1830).