Did he love to swim? Just the opposite! (7)
I believe the answer is:
leander
'did he love to swim? just the opposite' is the definition.
The definition suggests a singular noun which matches the answer.
'did he' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'der' and 'der' is found in the answer.
The remaining letters 'lean' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for leander that I've seen before include "In Greek mythology, Hero's beloved who drowned in a lake" , "man who went under" , "youth who drowned" , "Heroic lover" , "Hero's lover; rowing club" .)