Check to board earlier vessel (8)
I believe the answer is:
schooner
'vessel' is the definition.
(type of ship)
'check to board earlier' is the wordplay.
'check' becomes 'ch' (abbreviation).
'to board' indicates putting letters inside (inserted letters come on board).
'earlier' becomes 'sooner' (synonyms).
'ch' put within 'sooner' is 'SCHOONER'.
(Other definitions for schooner that I've seen before include "Two-master; a glass" , "Measure for sherry or kind of sailing ship" , "In the main it is" , "boat" , "Type of glass" .)