Jason’s ship (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">jason's ship</span>' is the definition.<br/ ><span class="explanation-format__explanation">(ship in Greek myth)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for argo that I've seen before include "Ancient ship" , "Constellation; ship" , "Old craft" , "Transport to find the Golden Fleece" , "Mythological ship" .)