Search Result for "seaweed": 
Wordnet 3.0

NOUN (1)

1. plant growing in the sea, especially marine algae; 



The Collaborative International Dictionary of English v.0.48:

Seaweed \Sea"weed`\, n.
   1. Popularly, any plant or plants growing in the sea.
      [1913 Webster]

   2. (Bot.) Any marine plant of the class Algae, as kelp,
      dulse, Fucus, Ulva, etc.
      [1913 Webster]


WordNet (r) 3.0 (2006):

seaweed
    n 1: plant growing in the sea, especially marine algae