Actually it was originally "champing" – to grind or gnash teeth. The "chomping" (to bite) alternative cropped up more recently as people misheard and misunderstood, but it's generally accepted as an alternative now.

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kortilla an hour ago | parent [-]

It’s actually accepted as the primary now and telling people about “champing” is just seen as archaic.

	▲	danpalmer an hour ago \| parent [-]
		Do you have a source on this, or a definition for what it means to be "primary" here? All I can find is sources confirming that "champing" is the original and more technically correct, but that "chomping" is an accepted variant.