Powerful feller shackles a wife (8)
I believe the answer is:
chainsaw
'powerful feller' is the definition.
(something which might fell trees)
'shackles a wife' is the wordplay.
'shackles' becomes 'chains' (chain is a kind of shackle).
'wife' becomes 'w'.
'chains'+'a'+'w'='CHAINSAW'
(Other definitions for chainsaw that I've seen before include "Powered cutter" , "Power tool" , "Tree-lopper's tool" , "woodcutter?" , "Texas massacre tool" .)