Audience set off in passenger ships (9)
I believe the answer is:
listeners
'audience' is the definition.
(people listening to something)
'set off in passenger ships' is the wordplay.
'off' indicates anagramming the letters.
'in' indicates putting letters inside.
'passenger ships' becomes 'liners' (I've seen this in another clue).
'set' anagrammed gives 'ste'.
'ste' placed into 'liners' is 'LISTENERS'.
(Other definitions for listeners that I've seen before include "Those who hear" , "Performers of tap" , "They follow advice" , "The audience" , "Hearers" .)