Cold? Once salve works, recover (10)
I believe the answer is:
convalesce
'recover' is the definition.
(I've seen this before)
'cold? once salve works' is the wordplay.
'cold?' becomes 'c' (eg on taps).
'works' indicates anagramming the letters.
'once'+'salve'='oncesalve'
'oncesalve' is an anagram of 'onvalesce'.
'c'+'onvalesce'='CONVALESCE'
(Other definitions for convalesce that I've seen before include "Improve" , "Recover after an illness" .)