Individual’s dreadfully insolent gesture at first (9)
I believe the answer is:
singleton
'individual's' is the definition.
(someone who is single)
'dreadfully insolent gesture at first' is the wordplay.
'dreadfully' is an anagram indicator (a dreadful spelling).
'at first' suggests taking the first letters.
The first letter of 'gesture' is 'g'.
'insolent'+'g'='insolentg'
'insolentg' is an anagram of 'SINGLETON'.
(Other definitions for singleton that I've seen before include "One of a kind" , "free spirit" , "spinster or bachelor?" , "One club maybe" , "in club, maybe, all alone" .)