Pleasant about egghead member of the family (5)
I believe the answer is:
niece
'member of the family' is the definition.
(I've seen this in another clue)
'pleasant about egghead' is the wordplay.
'pleasant' becomes 'nice' (associated in meaning).
'about' is an insertion indicator.
'egghead' becomes 'e' (head letter of 'egg').
'nice' going around 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "Female family member" , "Kinswoman" , "Preparation for curdling milk" , "Brother or sister's daughter" , "Young female relative" .)