Playing Uno with Kathy? You shouldn’t have! (5,3)
I believe the answer is:
thank you
'shouldn't have' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'playing uno with kathy?' is the wordplay.
'playing' indicates an anagram.
'with' is a charade indicator (letters next to each other).
'uno' put after 'kathy' is 'kathyuno'.
'kathyuno' is an anagram of 'THANK-YOU'.
'you' acts as a link.
Can you help me to learn more?
(Other definitions for thank you that I've seen before include "Ta" , "Much obliged!" , "Conventional expression of gratitude" , "Polite acknowledgment" , "Cheers" .)