Chastise wife that's turned against child (5)
I believe the answer is:
birch
'chastise' is the definition.
(thesaurus)
'wife that's turned against child' is the wordplay.
'wife' becomes 'rib'.
'that's turned' says the letters should be written in reverse.
'against' says to put letters next to each other.
'child' becomes 'ch' (abbreviation for child).
'rib' reversed gives 'bir'.
'bir'+'ch'='BIRCH'
(Other definitions for birch that I've seen before include "'Slender tree, the bark could be silver (5)'" , "Tree with silvery bark" , "Type of tree" , "Flogging rod" , "Tree bearing catkins" .)