"delightful or excellent person or thing" (often used ironically), 1935, American English, from an earlier adjective (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 French carrosse de diligence (see diligence).[dilly etymology, dilly origin, 英语词源]