any of an order (Actiniaria) of flowerlike, anthozoan sea polyps having a firm, gelatinous, often large, body without a skeleton, topped with petal-like tentacles: they are often brightly colored and live attached to rocks, pilings, etc.
See sea anemone in American Heritage Dictionary 4
noun
Any of numerous flowerlike marine coelenterates of the class Anthozoa, having a flexible cylindrical body and tentacles surrounding a central mouth.