Not a horse but a girl backs it (3)

I believe the answer is:

yak

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'it' is the definition.
The definition suggests a singular noun which matches the answer.

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(Other definitions for yak that I've seen before include "Himalayan bovine" , "Long-haired ox of SE Asia" , "Gossip (sl)" , "Talk incessantly" , "Blabber" .)

I've seen this clue in The Globe and Mail.

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