Language in ship seeking the Golden Fleece for Troy (5)
I believe the answer is:
argot
'language' is the definition.
(argot can mean jargon or slang)
'ship seeking the golden fleece for troy' is the wordplay.
'ship seeking the golden fleece' becomes 'Argo' (as in Jason and the Argonauts).
'for' is a charade indicator (letters next to each other).
'troy' becomes 't'.
'argo'+'t'='ARGOT'
'in' acts as a link.
(Other definitions for argot that I've seen before include "Jargon - patois" , "Slang, patois" , "Slang for a groat (5)" , "Father or mother" , "Slang of a particular group, originally thieves" .)