Reindeer in peril, about to be substituted for good (6)

I believe the answer is:

dancer

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But I can't explain it at all! Could you help me understand?

(Other definitions for dancer that I've seen before include "See 25" , "Terpsichorean" , "Ballet performer" , "One in the same team as, say, Rudolf" , "Entertainer" .)

I've seen this clue in The Times.

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