With endless ingenuity (3)
I believe the answer is:
wit
'ingenuity' is the definition.
(wit can mean cleverness or ingenuity)
'with endless' is the wordplay.
'endless' means to remove the last letter.
'with' with its final letter removed is 'WIT'.
(Other definitions for wit that I've seen before include "Intelligence; humorist" , "Comedian" , "Funny person" , "Ingenuity; wag" , "Drollness, humour" .)