E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Theon’s Tooth.
The bite of an ill-natured or carping critic. “Dente Theonino circumrodi,” to be nastily aspersed. (Horace: Epistles, i. 18, 82.) Theon was a carping grammarian of Rome.
