Thomas Hewitt Key (March 20, 1799 – November 29, 1875), English classical scholar, was born in London.

He was educated at St John's and Trinity Colleges, Cambridge, and graduated 19th wrangler in 1821. From 1825 to 1827 he was professor of mathematics in the university of Virginia, and after his return to England was appointed (1828) professor of Latin in the newly founded university of London.

In 1832 he became joint headmaster of the school founded in connection with that institution; in 1842 he resigned the professorship of Latin, and took up that of comparative grammar, together with the undivided headmastership of the school. These two posts he held till his death.

Key is best known for his introduction of the crude-form (the uninflected form or stem of words) system, in general use among Sanskrit grammarians, into the teaching of the classical languages. This system was embodied in his Latin Grammar (1846). In Language, its Origin and Development (1874), he upholds the onomatopoeic theory.

Key was prejudiced against the German Sanskritists, and the etymological portion of his Latin Dictionary, published in 1888, was severely criticized on this account. He was a member of the Royal Society and president of the Philological Society , to the Transactions of which he contributed largely.

See Proceedings of the Royal Society, vol. xxiv. (1876); Robinson Ellis in the Academy (Dec. 4, 1875); JP Hicks, T Hewitt Key (1893), where a full list of his works and contributions is given.