Clean, cold, bitter outside (5)
I believe the answer is:
scour
'clean' is the definition.
(thesaurus)
'cold bitter outside' is the wordplay.
'cold' becomes 'c' (eg on taps).
'bitter' becomes 'sour' (I've seen this before).
'outside' indicates putting letters inside.
'c' inserted inside 'sour' is 'SCOUR'.
(Other definitions for scour that I've seen before include "Full" , "Clean by abrasion" , "Clean - scout" , "scrub and scrape" , "Clean by rubbing with an abrasive" .)