One of billions vacuous buffoon, I recall, wasted? (5,4)
I believe the answer is:
brain cell
'one of billions' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'vacuous buffoon i recall wasted?' is the wordplay.
'vacuous' means to remove the middle letters.
'wasted?' is an anagram indicator.
'buffoon' with its middle removed is 'bn'.
'bn'+'i'+'recall'='bnirecall'
'bnirecall' anagrammed gives 'BRAIN CELL'.
Can you help me to learn more?
(Other definitions for brain cell that I've seen before include "Thinking unit?" , "Thoughtful unit" .)