Vacancies on trendy rocket (9)
I believe the answer is:
spaceship
'rocket' is the definition.
(thesaurus)
'vacancies on trendy' is the wordplay.
'vacancies' becomes 'spaces'.
'on' says to put letters next to each other.
'trendy' becomes 'hip' (I've seen this before).
'spaces'+'hip'='SPACESHIP'
(Other definitions for spaceship that I've seen before include "Interplanetary craft" , "orbiter, perhaps" , "craft going far?" , "Transport that's out of this world" , "long-distance vessel" .)