Finch is back by hide (6)
I believe the answer is:
siskin
'finch' is the definition.
(siskin is a kind of finch)
'is back by hide' is the wordplay.
'back' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'hide' becomes 'skin' ('skin' can be a synonym of 'hide'**).
'is' in reverse letter order is 'si'.
'si'+'skin'='SISKIN'
(Other definitions for siskin that I've seen before include "Yellow-green finch" , "Yellow-green bird" , "Finch akin to canary" , "Breed of finch" , "Singer" .)