Measure of Gallic avarice, endless (6)
I believe the answer is:
degree
'measure' is the definition.
(I know that degree is a type of angular unit)
'of gallic avarice endless' is the wordplay.
'of gallic' becomes 'de'.
'avarice' becomes 'greed' (synonyms).
'endless' means to remove the last letter.
'greed' with its final letter taken away is 'gree'.
'de'+'gree'='DEGREE'
(Other definitions for degree that I've seen before include "Rank" , "Scholastic award for a grade on a scale" , "See 13" , "'Grade, step or award (6)'" , "Graduate's qualification" .)