Frank's cousin (4)
I believe the answer is:
brat
'frank's cousin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for brat that I've seen before include "Nasty child" , "child - that's a nuisance" , "Irritating youngster" , "Ill-behaved child" , "An obnoxious or spoiled child" .)