Small step in room (5)
I believe the answer is:
space
'room' is the definition.
(thesaurus)
'small step' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'step' becomes 'pace' ('pace' can be a synonym of 'step').
's'+'pace'='SPACE'
'in' acts as a link.
(Other definitions for space that I've seen before include "Gap between words" , "Interstellar region" , "Empty area, may be outer" , "Free area" , "Expanse" .)