Quick butcher's severing grand knight's arm (5)

I believe the answer is:

lance

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'arm' is the definition.
(lance is a kind of arm)

I cannot understand how the remainder of the clue works.

(Other definitions for lance that I've seen before include "A horse soldier's spear" , "Shafted weapon used on horseback" , "Long weapon; prick" , "Pointed instrument" , "Knightly weapon" .)

I've seen this clue in The Times.

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