He was a lopper of sweaters! (7)
I believe the answer is:
'he' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?
'a lopper of sweaters' is the wordplay.
I cannot really understand how this works, but
'a' could be 'one' and 'one' is found in the answer.
'of' could be 'o' and 'o' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'was' acts as a link.
Can you help me to learn more?
(Other definitions for spooner that I've seen before include "Oxford academic notable for mixing up his syllables when talking, d. 1930" , "Revd W.A.- was famed for his errors in speech" , "Original transposer of initial letters in speech" , "One who gave his name to a transposition of sounds in speech" , "Initial-transposing clergyman" .)