Adult in blazer needing a bath (5)
I believe the answer is:
sauna
'bath' is the definition.
(I've seen this before)
'adult in blazer needing a' is the wordplay.
'adult' becomes 'a' (abbreviation).
'in' means one lot of letters goes inside another.
'blazer' becomes 'sun' (I've seen this in other clues).
'needing' is a charade indicator (letters next to each other).
'a' inserted inside 'sun' is 'saun'.
'saun'+'a'='SAUNA'
(Other definitions for sauna that I've seen before include "A Scandinavian steam bath" , "Where one is sweaty" , "Form of steam bath" , "Room for steam bath" , "Type of bath" .)