Too empty-headed even to make a joke? (7)
I believe the answer is:
witless
'too empty-headed' is the definition.
'witless' can be an answer for 'empty-headed' (thesaurus). I'm unsure of the 'too' bit.
'even to make a joke?' is the wordplay.
I cannot quite understand how this works, but
'joke?' could be 'wit' (joke is a kind of wit) and 'wit' is found in the answer.
The remaining letters 'less' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for witless that I've seen before include "Lacking sense, understanding or judgment" , "Daft" , "Out of one's mind (maybe scared)" , "Foolish, stupid" .)