Well-trained, I’d been to swimming (8)
I believe the answer is:
obedient
'well-trained' is the definition.
Both the definition and answer are adjectives.
Perhaps they are linked in a way I don't understand?
'i'd been to swimming' is the wordplay.
'swimming' is an anagram indicator (letters swim around into a new order).
'id'+'been'+'to'='idbeento'
'idbeento' with letters rearranged gives 'OBEDIENT'.
Can you help me to learn more?
(Other definitions for obedient that I've seen before include "Passive" , "co-operative?" , "Doing as one's told" , "Ready to agree" , "Complying with orders" .)