Puzzle involving puns, only shortened (7)
I believe the answer is:
nonplus
'puzzle' is the definition.
(I know that puzzle can be written as nonplus)
'involving puns only shortened' is the wordplay.
'involving' indicates anagramming the letters.
'shortened' means to remove the last letter.
'puns'+'only'='punsonly'
'punsonly' with its last letter taken away is 'punsonl'.
'punsonl' anagrammed gives 'NONPLUS'.
(Other definitions for nonplus that I've seen before include "Confound, bewilder" , "nothing if not negative?" , "Cause dismay" , "Utterly confuse" , "Surprise and confuse" .)