He deprives many of a happy ending (3)
I believe the answer is:
man
'he' is the definition.
(I've seen this in another clue)
'deprives many of a happy ending' is the wordplay.
I cannot quite understand how this works, but
'many' could be 'm' (Roman numeral for a thousand) and 'm' is found within the answer.
'a' could be 'an' and 'an' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for man that I've seen before include "Irish Sea isle" , "Fellow" , "Vassal; chess piece" , "knight, perhaps?" , "Homo sapiens" .)