Feigns hesitation when surrounded by fools (7)
I believe the answer is:
assumes
'feigns' is the definition.
(I know this)
'hesitation when surrounded by fools' is the wordplay.
'hesitation' becomes 'um' (um is said in hesitation).
'when surrounded by' means one lot of letters goes inside another.
'fools' becomes 'asses' (ass can mean a foolish person).
'um' inserted into 'asses' is 'ASSUMES'.
(Other definitions for assumes that I've seen before include "Puts on; accepts" , "Take to be the case" , "Takes to be the case" , "Takes for granted or puts on" , "dons" .)