'Seaweed' definitions:

Definition of 'seaweed'

From: WordNet
noun
Plant growing in the sea, especially marine algae

Definition of 'Seaweed'

From: GCIDE
  • 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]