A dashed dotty signalling system? (5)

I believe the answer is:

morse

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'system?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

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

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(Other definitions for morse that I've seen before include "Walrus - TV detective" , "Code; TV detective" , "Colin Dexter's fictional detective" , "One who enjoyed solving code" , "Endeavour" .)

I've seen this clue in the Evening Standard.

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