[cir.rus] n, pl cir.ri [NL, fr. L, curl] (1708) 1: tendril
2: a slender usu. flexible animal appendage: as a: an arm of a barnacle b: a filament of a crinoid c: a fused group of cilia functioning like a limb on some protozoans d: the male copulatory organ of various invertebrate animals
3: a wispy white cloud usu. of minute ice crystals formed at altitudes of 20,000 to 40,000 feet (6,000 to 12,000 meters)--see cloud illustration