Oscillaria \Os`cil*la"ri*a\, n. [NL., fr. L. oscillare to swing.] (Bot.) A genus of dark green, or purplish black, filamentous, fresh-water alg[ae], the threads of which have an automatic swaying or crawling motion. Called also {Oscillatoria}. Oscillatoria \Os`cil*la*to"ri*a\, n. pl. [NL. See {Oscillatory}.] (Bot.) Same as {Oscillaria}.