Headgear provided by mum, temperature rising (3)
I believe the answer is:
tam
'headgear' is the definition.
(tam is a kind of headgear)
'by mum temperature rising' is the wordplay.
'by' is a charade indicator (letters next to each other).
'mum' becomes 'ma' ('ma' can be a synonym of 'mum').
'temperature' becomes 't' (abbreviation).
'rising' shows that the letters should be reversed in order (going up in a down clue).
'ma' put next to 't' is 'mat'.
'mat' written backwards gives 'TAM'.
'provided' is the link.
(Other definitions for tam that I've seen before include "Headgear" , "'Woollen cap of Scottish origin, in short (3)'" , "TV audience ratings" , "Scots hat" , "Index rating for TV watching" .)