Instrument for fixing stair (5)
I believe the answer is:
sitar
'instrument' is the definition.
(sitar is a type of musical instrument)
'fixing stair' is the wordplay.
'fixing' is an anagram indicator.
'stair' with letters rearranged gives 'SITAR'.
'for' is the link.
(Other definitions for sitar that I've seen before include "music-maker" , "Lasting from morning to night" , "music producer" , "Hindu stringed instrument" , "Indian stringed instrument" .)