I first deal with extra-vacuous clue (4)
I believe the answer is:
idea
'clue' is the definition.
(I've seen this before)
'i first deal with extra-vacuous' is the wordplay.
'first deal' becomes 'd' (1st letter of 'deal').
'with' means one lot of letters go next to another.
'vacuous' means to remove the middle letters.
'extra' with its middle removed is 'ea'.
'i'+'d'+'ea'='IDEA'
(Other definitions for idea that I've seen before include "A suspicion of" , "Thought; concept" , "Plato's Form is" , "Notion, belief" , "Thought or notion (4)" .)