"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).
Entries linking to dilly
diligence n.
mid-14c., "constant and earnest effort to accomplish what is undertaken," from Old French diligence "attention, care; haste, speed" and directly from Latin diligentia "attentiveness, carefulness," from diligentem (nominative diligens) "attentive, assiduous, careful," present-participle adjective from diligere "single out, value highly, esteem, prize, love; aspire to, be content with, appreciate," originally "to pick out, select," from dis- "apart" (see dis-) + legere "choose, gather," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')."
Sense evolved through time from "love" through "attentiveness" to "carefulness" to "steady effort." Legal sense "attention and care due from a person in a given situation" is from 1620s. From the secondary French sense comes the old useage of diligence for "public stage coach" (1742; dilly for short), from a French shortening of carrosse de diligence.
