Overall you have on to provide warmth (7)
I believe the answer is:
blanket
'overall' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for blanket that I've seen before include "All-encompassing bedding?" , "coverage" , "Woollen bed cover" , "Spread over as with bedclothes" , "Covering (on bed)" .)