actinia
noun
ac·tin·ia
ak-ˈti-nē-ə
1
capitalized in some classifications : a genus of sea anemones nearly coextensive with the order Actiniaria
2
plural actiniae
ak-ˈti-nē-ˌē
or actinias : any sea anemone or related animal 
Word History
Etymology
borrowed from New Latin, from Greek aktīn-, aktís "ray, beam" + New Latin -ia -ia entry 1
First Known Use
1752, in the meaning defined at sense 1