"delightful or excellent person or thing" (often used ironically), 1935, from an earlier adj. (1909), perhaps from the first syllable of delightful or delicious, or related to the nursery word for "duck." Dilly was also slang for a stagecoach (1818), from Fr. carrosse de diligence. The noun is 1935. Dilly-dally is from 1741, a reduplication of dally.