dilly (n.)

"delightful or excellent person or thing" (often used ironically), 1935, American English, from an earlier adjective (1909), which is perhaps from the first syllable of delightful or delicious. Or perhaps the noun is related to the 19c. nursery word for "duck." Dilly was also slang for a stagecoach (1818), from French carrosse de diligence (see diligence).