Swimmer closing in on rest (8)
I believe the answer is:
breather
'rest' is the definition.
(I know that breather is a type of rest)
'swimmer closing in on' is the wordplay.
I cannot quite see how this works, but
'on' could be 'at' (I've seen this in other clues) and 'at' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for breather that I've seen before include "One who inspires" , "A rest from work - rather be thus" , "Informally a pause for rest - or to take in air" , "Short pause for rest" , "A rest - lung?" .)