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1.
The correct spelling is shoo-in, usually with a hyphen. It has been known in that spelling and with the meaning of a certain winner from the 1930s. It came from horse racing, where a shoo-in was the winner of a rigged race.

In turn that seems to have come from the verb shoo, meaning to drive a person or an animal in a given direction by making noises or gestures

These day's the term is associated with short odd's favourites in any sport
Australia are shoo-in's for the cricket world cup
by TheDaddy April 25, 2007