oscillatory

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.

Word History: The rather dry word oscillate may become a bit less dry when we learn its story. It is possible that it goes back to the Latin word ōscillum, a diminutive of ōs, "mouth," meaning "small mouth." In a passage in the Georgics, Virgil applies the word to a small mask of Bacchus hung from trees to move back and forth in the breeze. From this word ōscillum may have come another word ōscillum, meaning "something, such as a swing, that moves up and down or back and forth." And this ōscillum was the source of the verb ōscillāre, "to ride in a swing," and the noun (from the verb) ōscillātiō, "the action of swinging or oscillating." The words have given us, respectively, our verb oscillate, first recorded in 1726, and our noun oscillation, first recorded in 1658. The next time one sees something oscillating, one might think of that small mask of Bacchus swinging from a pine tree in the Roman countryside.