Bird near foot of mast on vessel (8)
I believe the answer is:
nightjar
'bird' is the definition.
(nightjar is a kind of bird)
'near foot of mast on vessel' is the wordplay.
'near' becomes 'nigh' (similar in meaning).
'foot of' says to take the final letters.
'on' says to put letters next to each other.
'vessel' becomes 'jar' (type of container).
The last letter of 'mast' is 't'.
'nigh'+'t'+'jar'='NIGHTJAR'
(Other definitions for nightjar that I've seen before include "Noct. bird (of harsh cry)" , "Nocturnal bird with harsh cry" , "Winger" , "flier" , "Nocturnal bird of swift family" .)