Northern hauliers St Nicholas employs? (8)

I believe the answer is:

reindeer

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'northern hauliers st' is the definition.
The definition suggests a singular noun which matches the answer.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for reindeer that I've seen before include "Domesticated animals" , "Beasts of the Arctic" , "for travellers from Lapland" , "Antlered subarctic creature" , "wild animal" .)

I've seen this clue in The Times.

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