Vessel or military vehicle on a road (7)
I believe the answer is:
tankard
'vessel' is the definition.
(tankard is a kind of vessel)
'military vehicle on a road' is the wordplay.
'military vehicle' becomes 'tank' (armoured vehicle).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'road' becomes 'rd' (abbreviation).
'tank'+'a'+'rd'='TANKARD'
'or' is the link.
(Other definitions for tankard that I've seen before include "something to drink from" , "Drinking vessel with a handle" , "A drinking mug with handle" , "Drank at (anag)" , "One-handled beer mug" .)