Legendary vessel making a right turn (4)
I believe the answer is:
'legendary vessel' is the definition.
(I've seen this in another clue)
'a right turn' is the wordplay.
'a right' becomes 'ar' (I've seen this in other clues).
'turn' becomes 'go' (a person's move in a board game).
'making' is the link.
(Other definitions for argo that I've seen before include "Jason's vessel" , "ancient boat" , "Stars once recognised in the south" , "Mythological ship" , "Agro about the constellation" .)