champ vs. chomp (at the bit). A short history.

In summary: champ is older as a verb in its own right, by anything between 51 and 183 years (depending on which source you go by); ‘the dictionaries’ agree that chomp is a by-form of champ; three major English dictionaries define chomp by reference back to champ; chomp in conjunction with bit is actually recorded earlier (1645) than champ at the bit, and the subsequent OED citation for chomp also includes the word bit; and Merriam-Webster shows an intransitive chomp meaning – ‘to be eager (to do)’ – that neither Collins nor the OED does.