1Zoology. Any of various echinoderms with multiply-branched arms, especially basket stars such as Gorgonocephalus; (formerly also) †the crinoid Cenocrinus asteria (formerly known as Pentacrinus caputmedusae) ( obsolete ).
2A South African spurge, Euphorbia caput-medusae, with many long intertwining stems.
Origin
Mid 16th century (in an earlier sense). From the genitive of Medusa + head.