Hide second family (4)
I believe the answer is:
skin
'hide' is the definition.
(a hide is an animal skin)
'second family' is the wordplay.
'second' becomes 's' (common abbreviation).
'family' becomes 'kin' (synonyms).
's'+'kin'='SKIN'
(Other definitions for skin that I've seen before include "Swindle" , "Outer surface" , "Surface layer" , "Fell" , "Outer layer of tissue" .)