www.alphadictionary.com

Interesting that you consider shoo a little known word. We use it around here frequently, and I've heard it all my life. But by far the principal meaning of the word refers to shooing away a cat a fly, or a kid. Never connected it to gambling. And of course there's always shoo-fly pie! (And Apple pound Dowdie…) therefore a shoo-in would be so obvious a winner that one would brush away any other possibility.

I'm just old school, I guess. I prefer "shoo-" and "strait-". I also say "font of all knowledge" rather than "fount" mainly because the word font leads to the Spanish word "fuente", which means "source". That's just me.