Pronunciation: (sir'us),[key] —n., —pl.cir•rusfor 1,cir•riPronunciation: (sir'ī)[key]for 2, 3. 1. Meteorol. a. a cloud of a class characterized by thin white filaments or narrow bands and a composition of ice crystals: of high altitude, ab. 20,000–40,000 ft. (6000–12,000 m).
b. a cirriform cloud.
2. Bot.a tendril.
3. Zool. a. a filament or slender appendage serving as a foot, tentacle, barbel, etc.
b. the male copulatory organ of flatworms and various other invertebrates.