Room for a rocket? (5)
I believe the answer is:
space
This clue is a double definition.
'room' is the first definition.
(thesaurus)
'a rocket?' is the second definition.
(space rocket is a kind of rocket)
'for' is the link.
(Other definitions for space that I've seen before include "sci-fi theme" , "Blank" , "Interstellar region" , ""The final frontier"" , "Expanse" .)