Stephenson dismisses female family member (7)
I believe the answer is:
stepson
'family member' is the definition.
(son of one's spouse)
'stephenson dismisses female' is the wordplay.
'dismisses' is a deletion indicator.
'female' becomes 'hen' (female chicken).
'stephenson' with 'hen' removed is 'STEPSON'.
(Other definitions for stepson that I've seen before include "No pests about this relation by marriage" , "No pests for male issue of spouse - but not of self" , "unrelated issue" , "Spouse's child from previous marriage" , "Male offspring of partner's former marriage" .)