Moving stair perhaps (5)
I believe the answer is:
astir
'moving' is the definition.
(I've seen this before)
'stair perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'stair' with letters rearranged gives 'ASTIR'.
(Other definitions for astir that I've seen before include "Starting to move" , "This isn't still" , "Up and about -- is art (anag)" , "Excitedly moving" , "abroad" .)