Relative is wasted being out of head (4)
I believe the answer is:
aunt
'relative' is the definition.
(aunt is a kind of relative)
'wasted being out of head' is the wordplay.
'wasted' becomes 'gaunt' (synonyms).
'being out of head' means to remove the first letter (the head letter is removed).
'gaunt' with its initial letter removed is 'AUNT'.
'is' is the link.
(Other definitions for aunt that I've seen before include "Family relative" , "Family member" , "Charley's in play?" , "Charley's ___ , farce staged in London in 1892, revived and adapted ever since" , "Blood relative" .)