Crossword Genius

Being superstitious, a muleteer has one (6)

Ross

I believe the answer is:

amulet

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

I can't explain the remainder of the clue.

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(Other definitions for amulet that I've seen before include "lucky defender" , "Charm warding off evil" , "Charm protecting against evil" , "Thing worn as charm against evil" , "that's charming" .)

I've seen this clue in the Evening Standard.
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