A naturist ultimately had lost interest in wearing clothes (7)
I believe the answer is:
attired
'wearing clothes' is the definition.
(I've seen this before)
'a naturist ultimately had lost interest' is the wordplay.
'ultimately' suggests the final letters.
'had' means one lot of letters go next to another.
'lost interest' becomes 'tired' (I can't justify this - if you can you should believe this answer much more).
The final letter of 'naturist' is 't'.
'a'+'t'+'tired'='ATTIRED'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for attired that I've seen before include "Dressed or clothed" , "Wearing clothes" , "surrounded by duds" , "Turned out" , "got up" .)