Mean enough to put learner in great unhappiness (7)
I believe the answer is:
miserly
'mean' is the definition.
(mean can mean miserly or ungenerous)
'enough to put learner in great unhappiness' is the wordplay.
I cannot really see how this works, but
'learner' could be 'l' (as in a learner driver with L-plates on their car) and 'l' is found within the answer.
'unhappiness' could be 'misery' (misery is a kind of unhappiness) and 'misery' is present in the remaining letters.
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 miserly that I've seen before include "Mean, tight" , "Parsimonious" , "Niggardly" , "Stingy" , "Paltry" .)