Bird arrives in vessel (6)
I believe the answer is:
parrot
'bird' is the definition.
(I know that parrot is a type of bird)
'arrives in vessel' is the wordplay.
'arrives' becomes 'arr' (abbreviation used in transport).
'in' means one lot of letters goes inside another.
'vessel' becomes 'pot' (type of container).
'arr' inserted inside 'pot' is 'PARROT'.
(Other definitions for parrot that I've seen before include "Brightly coloured tropical bird" , "Tropical bird for Pat Orr" , "The bird can mimic sounds" , "Repeat without understanding" , "Imitate like tropical bird" .)