Crow flies, finally, into vessel (5)
I believe the answer is:
boast
'crow' is the definition.
(I know that crow is a more specific form of the action boast)
'flies finally into vessel' is the wordplay.
'finally' indicates one should take the final letters.
'into' means one lot of letters goes inside another.
'vessel' becomes 'boat' (boat is a kind of vessel).
The last letter of 'flies' is 's'.
's' inserted inside 'boat' is 'BOAST'.
(Other definitions for boast that I've seen before include "Show off" , "shot off the side wall" , "Proudly possess" , "something to brag about" , "Expression of excessive pride" .)