The vehicle is the word or image in a metaphor that carries the figurative comparison. It is the thing being described in a new, imaginative way, while the tenor is the idea or subject the poet really means. In the metaphor "time is a thief," thief is the vehicle.
Example
In the line "Her laugh was a silver bell in the dark,"
"silver bell" is the vehicle that helps describe the laugh.
Related Definitions
[n] a conveyance that transports people or objects
[n] a medium for the expression or achievement of something; "his editorials provided a vehicle for his political views"; "a congregation is a vehicle of group identity"