1. A river of southern England flowing about 340 km (210 mi) eastward to a wide estuary on the North Sea. Navigable for large ships as far as London, it is the principal commercial waterway of the country. In its upper course above Oxford it is often called Isis.
2. A river, about 260 km (160 mi) long, of southeast Ontario, Canada, flowing southwest to Lake St. Clair. In the War of 1812 Gen. William Henry Harrison defeated British and Native American forces in the Battle of the Thames (October 5, 1813).
Word History: The Roman name for the River Thames was Tamēsa or Tamēsis, and this name doubtless has its origins in the Celtic languages originally spoken in Great Britain, languages that were later widely replaced by Old English after the arrival of the Anglo-Saxons. The first mention of the Thames in the surviving literature of Old English occurs in a work from around 893, an abridged translation of the work of the late Roman historian Paulus Orosius. This translation is traditionally attributed to Alfred the Great, who translated many classics from Latin himself, but it was probably made by others as part of the ambitious program of translations that the king organized in order to further the spread of knowledge in his realm. In Alfred's time, the Old English name of the river was spelled Temese or Temes. The spellings of the name of the river with an h, such as Thamyse and Thames, are much later and first begin to appear in the early 1500s. Such spellings are examples of the kind of "learned" respelling that went on in English from the late Renaissance through the Enlightenment, when the prestige of Latin and Greek prompted scholars to "correct" the form of many English words. The a in Thames is etymologically correct, since the Latin forms had that vowel, but the h is a "learned" error, added in the mistaken belief that Thames derived from a Greek word, such as the name of a Greek river called the Thyamis. Such errors were common, and many words that had nothing to do with Greek were respelled to make them look Greek. In many cases, the pronunciations of these words changed accordingly, yielding what linguists call a spelling pronunciation; for example, author, from Latin auctor and not from a Greek word, is now pronounced with a (th), even though we would strictly expect it to be pronounced with a (t) instead. The pronunciation of Thames remained unchanged, however, providing an etymologically explicable example of the notorious discrepancy between English spelling and pronunciation.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.