Instrument to fix stair (5)
I believe the answer is:
sitar
'instrument' is the definition.
(sitar is a type of musical instrument)
'fix stair' is the wordplay.
'fix' indicates anagramming the letters.
'stair' is an anagram of 'SITAR'.
'to' acts as a link.
(Other definitions for sitar that I've seen before include "Large Indian lute" , "Indian string instrument" , "Lasting from morning to night" , "Astir with Indian long-necked lute" , "Plucked instrument" .)