Published in 2 volumes and an expanded edition was published in 1798. A treatise on the etymology of English words in which Tooke was one of the first to insist on the importance of studying Gothic and Anglo-Saxon philology.

"Easy to digest in its dialogue format, it is full of classical allusions and philosophical arguments, directed at a cultivated audience familiar with classical and modern languages and nicknamed the 'Botheration Dictionary'. Many of its ideas were wrong-headed, absurd or fanciful, but it was a pioneer work of philology, notable for the attention to Anglo-Saxon roots. Apart from establishing his credentials as a scholar, Tooke had other motives for compiling this work: venting his spleen and making money. The commentary and examples are laced with his prejudices against the political system and men of his day, and it earned him nearly £5000 altogether, an important consideration to a man who was always short of money." (P.D.G. Thomas, review of Gentleman Radical: A Life of John Horne Tooke 1736-1812, by Christina Bewley and David Bewley, Tauris, 297 pp., 1998, in LRB, 19 August 1999.)

Tooke was ordained to curacy in 1760. In 1769 he helped John Wilkes found the Bill of Rights Society, but broke with Wilkes in 1771 to create the Constitutional Society to agitate for parliamentary reform and independence for the American colonies. After Tooke promoted a subscription in 1778 for the relief of relatives of Americans 'murdered' at Lexington and Concord he was fined and imprisioned for a year. Between 1782 and 1790 he supported Pitt in pamphlets, he was tried but acquitted for high treason in 1794 and in 1801 was debarred as MP by a special act rendering clergy ineligible.