Ship that goes by land (7)

I believe the answer is:

coaster

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'ship' is the definition.
(coaster is a type of ship)

I don't understand how the rest of the clue works.

(Other definitions for coaster that I've seen before include "Small mat for glass" , "Mat to protect a table" , "Small table mat" , "Mat for decanter or glasses" , "Trading vessel" .)

I've seen this clue in The Globe and Mail.

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