Idly swimming in pool that's refined (8)
I believe the answer is:
ladylike
'refined' is the definition.
('ladylike' can be similar in meaning to 'refined')
'idly swimming in pool' is the wordplay.
'swimming' is an anagram indicator.
'in' is an insertion indicator.
'pool' becomes 'lake' (I've seen this before).
'idly' with letters rearranged gives 'dyli'.
'dyli' inserted into 'lake' is 'LADYLIKE'.
'that's' is the link.
(Other definitions for ladylike that I've seen before include "Appropriate to female decorum" , "Of a woman, refined and genteel" , "Genteel (not referring to gents)" , "Graciously feminine" , "Decorously feminine" .)