Sage Derby perhaps consumed by mother (7)
I believe the answer is:
mahatma
'sage' is the definition.
('mahatma' can be a synonym of 'sage')
'derby perhaps consumed by mother' is the wordplay.
'derby perhaps' becomes 'hat' (derby is a kind of hat).
'consumed by' indicates putting letters inside.
'mother' becomes 'mama' (mama is a kind of mother).
'hat' placed inside 'mama' is 'MAHATMA'.
(Other definitions for mahatma that I've seen before include "Gandhi's title" , "Hindu leader" , "Savant" , "Brahman sage" , "Wise fellow" .)