Peaty coal failed to start fire (6)

I believe the answer is:

ignite

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'fire' is the definition.
(thesaurus)

I don't understand the remainder of the clue.

(Other definitions for ignite that I've seen before include "Swan constellation" , "Combust" , "'Set alight, fire up (6)'" , "Put a match to" , "Spark off" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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