1
general::
Show impatience at being held back or delayed, as in The dismissal bell hadn't rung, but they were champing at the bit to leave. This term transfers the action of a horse that impatiently bites the bit in its mouth to human behavior. [Mid-1600s]
American Heritage Idioms
2
general::
Phrase(s): champ at the bit [and] chomp at the bit
1. Lit. [for a horse] to bite at its bit, eager to move along. • Dobbin was champing at the bit, eager to go. 2. Fig. to be ready and anxious to do something. • The kids were champing at the bit to get into the swimming pool. • The dogs were champing at the bit to begin the hunt.
McGrawhill's American Idioms And Phrasal Verbs