"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).
1. Don't dilly - dally ! Make up your mind!
2. Don't dilly dally, hurry up!
3. This little car is a real dilly!
4. I sicken at his dilly - dallying.
5. He often dilly - dallied in making up his mind, until it was too late.