Swimmer turned round, squinting (7)
I believe the answer is:
leering
'squinting' is the definition.
The answer and definition can be both to do with perception as well as being present participle verbs.
Maybe they are linked in a way I don't understand?
'swimmer turned round' is the wordplay.
'swimmer' becomes 'eel' (eel is a kind of aquatic vertebrate).
'turned' says the letters should be written backwards.
'round' becomes 'ring' (synonyms).
'eel' in reverse letter order is 'lee'.
'lee'+'ring'='LEERING'
Can you help me to learn more?
(Other definitions for leering that I've seen before include "appearing lascivious" , "Looking suggestively" , "giving the glad eye" , "Gazing lasciviously" , "Ogling" .)