Vessel used in embarkation (3)
I believe the answer is:
ark
'vessel' is the definition.
(ark is a kind of vessel)
'in embarkation' is the wordplay.
'in' says the answer is hidden in the clue.
'ARK' is hidden in the letters of 'embarkation'.
'used' acts as a link.
(Other definitions for ark that I've seen before include "Ancient shelter" , "Flood vessel; box (arch.)" , "old vessel" , "Great biblical boat" , "Ship built by Noah" .)