Green’s Dictionary of Slang

a dandy; a term of affectionate address.

1793		W. Macready Irishman in London II ii: Arrah! is it my own daffy-down-dilly you want, Maister Pat, to bring home? Oh thunder! Arrah be asy!
1812		J. Bell Jr. (ed.) Rhymes of Northern Bards 104: Wilt thou take my tokens? sweet daffa-down-dilly.
1840		E. Howard Jack Ashore III 273: It does my poor broken heart good to hear ye cuss that sodger – go it again, my daffy-down-dilly, and lay it on thick.
1845		J. Lindridge Sixteen-String Jack 68: Ha! my daffy-down-dilly, how are you?
1927		(con. 1835–40) P. Herring Bold Bendigo 215: I’m to be one of the bridesmaids dressed like Daffy-down-dilly in a green gown.