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os·cil·late (ŏsə-lāt)
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intr.v. os·cil·lat·ed, os·cil·lat·ing, os·cil·lates
1. To swing back and forth with a steady, uninterrupted rhythm.
2. To waver, as between conflicting opinions or courses of action; vacillate: "The court has oscillated over the decades from more liberal to less, more conservative to less, depending upon who was president at the time of vacancies" (Gordon J. Humphrey). See Synonyms at swing.
3. Physics To vary between alternate extremes, usually within a definable period of time.

[Latin ōscillāre, ōscillāt-, from ōscillum, something that swings back and forth, swing, probably from ōscillum, small mask of Bacchus, diminutive of ōs, mouth; see ōs- in the Appendix of Indo-European roots.]

oscil·lator n.
oscil·la·tory (-lə-tôrē) adj.

Word History: The history of the word oscillate shows how English words referring to technical or scientific concepts often come from Latin words describing everyday objects and ordinary life in ancient times. In a passage in his Georgics, a long poem celebrating rural life, the Roman poet Virgil describes how Bacchus is honored in the countryside by hanging small masks from pine trees. He uses the Latin word ōscillum (plural ōscilla) to refer to these hanging religious decorations, which were common in the ancient Roman world. The house of a wealthy Roman family was usually built around one or more courtyards or gardens enclosed by rows of columns, and in each space between these columns, an ōscillum was often hung. It is probable that this word ōscillum, "something that swings back and forth," is simply an extended use of the word ōscillum meaning "a small mouth, a small face" (a diminutive of ōs, "mouth"), since the swinging objects most often consisted of masks or tondi depicting faces. From the word ōscillum, "something that swings back and forth," the Romans derived the verb ōscillāre, "to ride in a swing," and the noun ōscillātiō, "the action of swinging." These are the sources of English oscillate and oscillation, words that entered English during the 1600s and 1700s as technical terms mainly used in scientific writings and similar works.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2016 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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