Greek characters sat back after end of voyage (4)
I believe the answer is:
etas
'greek characters' is the definition.
(I've seen this before)
'sat back after end of voyage' is the wordplay.
'back' shows that the letters should be reversed in order.
'after' says to put letters next to each other.
'end of' indicates one should take the final letters.
The last letter of 'voyage' is 'e'.
'sat' in reverse letter order is 'tas'.
'tas' after 'e' is 'ETAS'.
(Other definitions for etas that I've seen before include "who once did menial tasks in Japan?" , "Characters in Greece" , "lowly workers" , "Foreign characters" , "Makarios' letters" .)