First-class swimming in the pool (3-4)
I believe the answer is:
top-hole
'first-class' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'swimming in the pool' is the wordplay.
'swimming in' is an anagram indicator.
'the'+'pool'='thepool'
'thepool' with letters rearranged gives 'TOP-HOLE'.
Can you help me to learn more?
(Other definitions for top-hole that I've seen before include "Excellent" , "First-rate" .)