The Collaborative International Dictionary of English v.0.48:

Actinia \Ac*tin"i*a\, n.; pl. L. Actini[ae], E. Actinias.
   [Latinized fr. Gr. ?, ?, ray.] (Zool.)
      (a) An animal of the class Anthozoa, and family
          Actinid[ae]. From a resemblance to flowers in form
          and color, they are often called animal flowers and
          sea anemones. [See Polyp.].
      (b) A genus in the family Actinid[ae].
          [1913 Webster]

WordNet (r) 3.0 (2006):

Actinia
    n 1: a genus of sea anemone common in rock pools [syn:
         Actinia, genus Actinia]
    2: any sea anemone or related animal [syn: actinia,
       actinian, actiniarian]