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Know Your Phrase - The Meanings For Common Sayings and Phrases > T-Letter Sayings
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Phrases and Idioms
knowyourphrase.com - The Meanings and Origins For Several Common Idioms and Phrases
T
To give up; surrender.
This phrase is believed to come from boxing, where the coach, or perhaps a teammate, would literally throw a towel into the ring in ordr to signal that his fighter has been defeated; it was basically a way to surrender. This term has been around since the very start of the 1900s from what I could find.

For example, this expression is written in the Kalgoorlie Western Argus, July 1900, appearing in a short article under the title "BOXING:"

"The final was particularly interesting, both King and Sullivan evidently intending to arrive at the actual
result as quickly as possible. King's left hand, however, met his opponent time after time, and nearing
the end of the second round Sullivan was beaten out, his second throwing in the towel."

A recording of the phrase with its figurative meaning comes just three years later, written in the Sunday Times newspaper, August 1903:

"Teetotal Smith, our great Mayor, goes about looking much depressed since the poll, and is, I suspect,
half inclined to throw in the towel."
* I started to do some cardio exercises as an attempt to get myself back into shape, but I had to throw in the towel early after spraining my ankle.
Note: A phrase's origins are, much of the time, completely unclear. The origins you see listed are the plausible theories floating around for how or where an idiom came from, but may not necessarily be accurate. The quotes which have the phrase in them are the oldest written forms of the phrase I could find, but keep in mind that older recordings are probably out there somewhere. If you find an earlier citation than what I have, feel free to let me know!

Also, remember that just because you see a saying in an old book or newspaper, let's say from the year 1893, it does not mean the saying originates from that source. In all likelihood, if an expression is already in use in a book or newspaper, then it's probably older. Nevertheless, these old quotes serve as a way to show the reader how far back in history some of these sayings go.