|This article relies largely or entirely upon a single source. (June 2013)|
A hydronym (from Greek: ὕδωρ, hydor, "water" and ὄνομα, onoma, "name") is a proper name of a body of water. Hydronymy is the study of hydronyms and of how bodies of water receive their names and how they are transmitted through history. It can apply to rivers, lakes, and even oceanic elements.
More than most toponyms, as linguistic items hydronyms are very conservative, with successor peoples often retaining the name given a body of water. For example, Mississippi has passed from Native Americans to contemporary Americans (and then to other languages). The names of large rivers are especially conserved, while the local names of small streams are less so.
As an example of hydronymy as a historical tool Kenneth Jackson identified a river-name pattern against which to fit the story of the Anglo-Saxon invasion of Britain and the pockets of survival of native British culture. Even in the eastern area of the heaviest and early Saxon settlement, major rivers like the Thames and the Trent preserve their pre-Saxon names. Jackson constructed a river map of Britain that enabled three principal areas of English settlement: the river valleys draining eastward, where British survivals are limited to the largest rivers, and Saxon settlement was early and dense, the highland spine, and a third region in which British hydronyms apply even to the smaller streams.
Often a given body of water will have several entirely different names given to it by different peoples living along its shores. For example, Vltava and Moldau are the Czech and German names, respectively, for the same river in central Europe.
Hydronyms from various languages can all share a common etymon. For example, the Danube, Don, Dniester, Dnieper and Donets rivers all contain the Scythian name for "river" (cf. don, "river, water" in modern Ossetic).
It is possible for a toponym to become a hydronym: for example, the River Liffey takes its name from the plain on which it stands, called Liphe or Life; the river itself was originally called An Ruirthech. An unusual example is the River Cam - it was originally called the Granta, but when the town of Grantebrycge became Cambridge, the river's name changed to match the toponym.
- Jackson, Language and History in Early Britain, Edinburgh, 1953:220-23, summarized in H.R. Loyn, Anglo-Saxon England and the Norman Conquest , 2nd ed. 1991:7-9.