Screw up in audition for Superman? (5)
I believe the answer is:
titan
'for superman?' is the definition.
(thesaurus)
'screw up in audition' is the wordplay.
'screw up' becomes 'tighten' (I've seen this before).
'in audition' shows a homophone (sound like) (audition can mean hearing).
'tighten' sounds like 'TITAN'.
(Other definitions for titan that I've seen before include "Largest satellite of Saturn" , "Rhea, perhaps" , "primordial god" , "Taint in old Greek god" , "Giant -- rocket" .)