Take off before temperature plunges (6)
I believe the answer is:
divest
'take off' is the definition.
(thesaurus)
'before temperature plunges' is the wordplay.
'before' says to put letters next to each other.
'temperature' becomes 't' (abbreviation).
'plunges' becomes 'dives' ('dive' can be a synonym of 'plunge').
't' put after 'dives' is 'DIVEST'.
(Other definitions for divest that I've seen before include "Relieve (oneself of garment)" , "Strip (someone of clothing)" , "Undress" , "Strip, remove garments" , "Strip, denude" .)