Entry 1 sense Webster, 1913 Cyclostomi /(s?-kl?s"t?-m?)/ · Cy·clos·to·mi · IPA 01 n. pl. A glass of fishes having a suckerlike mouth, without jaws, as the lamprey; the Marsipobranchii. 1. A glass of fishes having a suckerlike mouth, without jaws, as the lamprey; the Marsipobranchii.(Zool.)