A number making a living in education (8)
I believe the answer is:
learning
'education' is the definition.
(I know that learning is a type of education)
'a number making a living' is the wordplay.
'a number' becomes 'L' (fifty in Roman numerals).
'making a living' becomes 'earning' (I've seen this in another clue).
'l'+'earning'='LEARNING'
'in' acts as a link.
(Other definitions for learning that I've seen before include "The gaining of knowledge" , "Lore" , "Discovering, finding out" , "Researching - scholarship" , "information" .)