Subject to miserly average (10,4)
I believe the answer is:
arithmetic mean
'average' is the definition.
(arithmetic mean is a kind of average)
'subject to miserly' is the wordplay.
I cannot quite see how this works, but
'subject' could be 'arithmetic' (arithmetic is a kind of subject) and 'arithmetic' is found in the answer.
'miserly' could be 'mean' (synonyms) and 'mean' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for arithmetic mean that I've seen before include "average amount" , "Ten is that of nine and eleven" .)