Champing at the bit was the original phrase, but chomping at the bit has been rapidly gaining ground since the 1930s. Here's some background and a memory trick I use to remember which phrase to use.
Mark E. from Portland, Oregon said he regularly comes across the phrase chomping at the bit, but he believes it should be champing at the bit.
The original phrase is, indeed, champing at the bit, but chomping at the bit emerged in America in the 1930s according to the Oxford English Dictionary and chomp has overtaken champ in common use.
A Google web search for chomping at the bit returns about twice as many results as a search for champing at the bit. Champing at the bit is still used just slightly more often than chomping at the bit in published books, but you can see chomping rapidly gaining ground in the Google Ngram chart that shows how often words and phrases are used.
Chomping has actually overtaken champing even in published books if you filter the search so that you look at just American English.
”Champ” is an older, more formal word that means to gnash or chew on something (as a horse would a bit), but we don't use champ much in American English. We are more likely to use the more informal word chomp, which is probably why people remember the phrase incorrectly.
Frequency alone doesn't make chomping at the bit correct, but most style guides and dictionaries I checked also refrain from going so far as to state that it is incorrect. This is language change at the point where you probably can’t win. No matter which form you choose, some people will think you got it wrong.
I'm going to stick with the original phrase, champing at the bit. Messages from people like Mark show that not everyone will overlook it if you decide to use the more popular chomping at the bit.
My memory tip is to remember which word to use by thinking of a horse named Champ.
That Quick and Dirty Tip was from my book 101 Misused Words You’ll Never Confuse Again.
Image courtesy of Shutterstock.