Dump by the wayside (5)

I believe the answer is:

ditch

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'dump' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

(Other definitions for ditch that I've seen before include "Dyke" , "side of field?" , "Moat" , "Excavated channel" , "Jettison" .)

I've seen this clue in the Evening Standard.

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