Jack Sprat's favourite daughter Eleanor on vacation, a keen swimmer (7)
I believe the answer is:
leander
'swimmer' is the definition.
(I've seen this before)
'jack sprat's favourite daughter eleanor on vacation a keen' is the wordplay.
I cannot really see how this works, but
'daughter' could be 'd' (genealogical abbreviation) and 'd' is found within the answer.
'a' could be 'an' and 'an' is found within the answer.
The remaining letters 'leer' is a valid word which might be clued in a way I don't see.
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 "Oarsmen" , "Heroic lover" , "In Greek legend, lover of Hero who drowned in the Hellespont" , "man who went under" , "In Greek myth, the lover of Hero" .)