Resolute aim to get hold of family member (9)
I believe the answer is:
insistent
'resolute' is the definition.
(thesaurus)
'aim to get hold of family member' is the wordplay.
'aim' becomes 'intent' (synonyms).
'to get hold of' means one lot of letters goes inside another.
'family member' becomes 'sis' (short for sister).
'intent' enclosing 'sis' is 'INSISTENT'.
(Other definitions for insistent that I've seen before include "Not giving up" , "Compelling attention" , "Demanding attention" , "Declaring or demanding emphatically" , "Unwilling to take "no" for an answer" .)