Slow Greek vessel following line (5)
I believe the answer is:
largo
'slow' is the definition.
(musical term)
'greek vessel following line' is the wordplay.
'greek vessel' becomes 'argo' (ship in Greek myth).
'following' is a charade indicator (letters next to each other).
'line' becomes 'l' (used when specifying particular lines from a poem).
'argo' put after 'l' is 'LARGO'.
(Other definitions for largo that I've seen before include "Deliberately" , "Slow piece of music" , "Broad and slow (mus.)" , "(Musically) slow in tempo and broad in manner" , "To be played slowly and broadly" .)