Hindu sage’s headgear adopted by graduate twice (7)
I believe the answer is:
mahatma
'hindu sage's' is the definition.
(term for a Hindu wiseman)
'headgear adopted by graduate twice' is the wordplay.
'headgear' becomes 'hat' (hat is a kind of headgear).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'graduate' becomes 'MA' (abbreviation for Master of Arts).
'twice' shows that letters should be duplicated.
'ma' duplicated is 'mama'.
'hat' going inside 'mama' is 'MAHATMA'.
(Other definitions for mahatma that I've seen before include "Great Soul, as Gandhi was called" , "Wise man" , "(Indian) holy person or sage" , "Holy person or sage in South Asia" , "Sage (as e.g. Gandhi)" .)