Giant back in pig, returned (7)
I believe the answer is:
goliath
'giant' is the definition.
(synonyms)
'back in pig returned' is the wordplay.
'back' becomes 'tail' (tail is a kind of back).
'in' is an insertion indicator.
'pig' becomes 'hog' (synonyms).
'returned' says the letters should be written backwards.
'tail' placed into 'hog' is 'htailog'.
'htailog' backwards is 'GOLIATH'.
(Other definitions for goliath that I've seen before include "an unusually tall person" , "Unusually large person" , "I got Hal a giant form the bible" , "David laid him low with slingshot" , "Biblical giant" .)