Caught doctor noshing missing small bun (7)
I believe the answer is:
chignon
'bun' is the definition.
(thesaurus)
'caught doctor noshing missing small' is the wordplay.
'caught' becomes 'c' (cricket abbreviation**).
'doctor' indicates an anagram.
'missing' is a deletion indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'noshing' with 's' taken away is 'nohing'.
'nohing' is an anagram of 'hignon'.
'c'+'hignon'='CHIGNON'
(Other definitions for chignon that I've seen before include "Arrangement of coil of hair" , "Coil of hair at the back of the head" , "Topknot" , "Hairstyle" , "Roll of hair worn at the back of the head" .)