Something or someone remarkable, excellent, or very entertaining. "Dilly," an American term from the early 1900s, possibly comes from the first syllable of the word "delightful" or "delicious." Primarily heard in US. I tell you, she's a real dilly. Out at 6 a.m. for a run, getting the kids off to school at 7, then out to manage the firm at 8. That film last night was a real dilly, I couldn't stop thinking about it all night.