Second rate room (5)
I believe the answer is:
space
'room' is the definition.
(thesaurus)
'second rate' is the wordplay.
'second' becomes 's' (common abbreviation).
'rate' becomes 'pace' (pace is a kind of rate).
's'+'pace'='SPACE'
(Other definitions for space that I've seen before include "Room for capes" , "Room; gap" , "Interstellar vacuum" , "sci-fi theme" , "Expanse" .)