oscillate: [18] Latin ōs originally meant ‘mouth’ (it was the source of English oral), but it was also used for ‘face’. Its diminutive form ōscillum ‘little face’ was applied to a mask depicting the god Bacchus that was hung up as a charm in vineyards, to be swung to and fro by the breeze. In due course its meaning broadened out to ‘swing’ generally, and a verb ōscillāre ‘swing’ was derived from it – whence English oscillate. => oral
