Mother could be odd ally (3,4)
I believe the answer is:
old lady
'mother' is the definition.
(thesaurus)
'could be odd ally' is the wordplay.
'could be' indicates anagramming the letters.
'odd'+'ally'='oddally'
'oddally' anagrammed gives 'OLD LADY'.
(Other definitions for old lady that I've seen before include "Wife or mother" , "Mum" , "Wife (informal)" , "Elderly woman" .)