Quickly get rid of a serpent (3)

I believe the answer is:

asp

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'serpent' is the definition.
(asp is a kind of serpent)

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

(Other definitions for asp that I've seen before include "Serpent" , "Snake found in spa" , "Small poisonous snake" , "Small viper" , "Snake seen in a spa, strangely" .)

I've seen this clue in The Irish Times.

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