Supportive of (3)
I believe the answer is:
pro
'supportive of' is the definition.
(as in being pro a person or cause)
This is the entire clue.
(Other definitions for pro that I've seen before include "Athelete who plays for pay" , "In favour of; advantage" , "Favouring the professional" , "With qualifications" , "Of argument, say, in favour of" .)