careen

Fascinating. I've often wondered why two such similar words ended up with the same (or a similar) definition.

"The word careen, 'to lurch or swerve while in motion,' illustrates a phenomenon that is frequently encountered when tracing the history of language: the development of a word can be influenced by other words of similar sound and related meaning, and similar words can exert mutual influence on each other.

"Careen was originally a nautical term meaning 'to lean a ship on its side for cleaning, caulking, or repairing.' The word comes from the French phrase en carène, meaning 'on the keel.' Carène is descended from the Latin word carina, 'keel, nutshell.' From the original sense relating to ships at rest, careen also came to be used of ships leaning to one side when sailing in the wind. In more recent times, the word careen has developed another sense, 'to rush headlong,' as in the sentence 'The truck went careening into the intersection,' and in other expressions in which the emphasis is on forward, rather than sideways, motion. In this sense the word careen has probably been influenced by the word career, 'to move or run at high speed.' Not only do the two verbs sound similar, but automobiles generally careen (that is, lurch or tip over) only when driven at high speed--in other words, when they are careering. Since the two verbs can be used in similar circumstances, the meaning of careen was probably extended to include that of career. This newer use of careen began to appear only in the 1920s. Many authorities on English usage, in fact, still recommend keeping careen, 'to lurch to the side,' distinct from career, 'to rush headlong forward.'"
--More Word Histories and Mysteries, from Aardvark to Zombie, from the editors of American Heritage (r) Dictionaries, 2006.