Vessel of an unfamiliar kind (3)
I believe the answer is:
ark
'vessel' is the definition.
(ark is a kind of vessel)
'of an unfamiliar kind' is the wordplay.
'of' says the answer is hidden in the clue.
'ARK' is hidden in the letters of 'unfamiliar kind'.
(Other definitions for ark that I've seen before include "Biblical vessel" , "Animal transporter" , "(E.g. poem) that tells a story" , "Rescue vessel" , "Coffer" .)