Family member's heading off: joy! (7)
I believe the answer is:
elation
'joy' is the definition.
(I know that elation is a type of joy)
'family member's heading off' is the wordplay.
'family member' becomes 'relation' (a relation or relative).
'heading off' means to remove the first letter.
'relation' with its first letter taken away is 'ELATION'.
(Other definitions for elation that I've seen before include "Feeling of intense delight" , "Toenail (anag) -- delight" , "exhibits successful pride" , "There's great joy" , "Feeling of delight or pride" .)