Note: A phrase's origins might not be known. In cases like this, what you will usually find on an idiom's page are the popular or plausible theories that exist for how a saying may have originated. Or, if not that, then I'll typically try to find the oldest known written form of the saying and list that. 

Anyways, if you are looking for more popular expressions, well, remember we have an alphabetical list containing plenty of them, and it's only a click away. We also have separate pages containing a list of all the sports and animal related phrases that have been added to this site so far, with a food one coming later. Just though I would, you know, mention that. Thanks for visiting!
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Common Phrase Origins and Meanings  |  E-Letter Idioms

Origins for the idiom Eat My Hat.
Speaking in a literal sense, would you really want to eat a hat? I wouldn't think so, considering they are made from materials such as cotton, linen, and leather; none of which sound particularly appetizing. Moreover, consuming a hat could be potentially dangerous, and it probably wouldn't taste very good either.

Leather, for instance, goes through a tanning process where it's treated with various chemicals that help strengthen it. The chemicals do their job of increasing the leather's durability, but I don't think you would want to eat that leather hat. Not to mention the amount of chewing involved would just be tiring. In short, just leave the thing on your head.

Indeed, nobody really wants to eat their hat. That's why this expression is only said when a person is feeling extremely confident about something.

This phrase makes an early appearance in several newspapers from the 19th century, one of them being the Iowa South West from the city of Bedford, 1876: 

    " 'If you are not Joe Kirby,' he said, 'I will eat my hat-I mean, of course-' 
      'Come, this is trifling. I say that you mistook me for some one else. What makes you think me Joe Kirby?'
      'Because you are.' "
* Susan is going to the dentist tomorrow, and since she takes such good care of her teeth, I'll eat my hat if she has a cavity!

* My friends must be feeling confident in my running ability since they said that they'll eat their hats if I manage to win the race tomorrow. 
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The meaning of the phrase Eat my Hat.
Having confidence in a specific outcome; being almost sure about something.

When a person makes a strong assumption, they may use popular idioms and phrases like this one to describe their feelings of near cerainty.
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