The Collaborative International Dictionary of English v.0.48:

Fucoid \Fu"coid\, n. (Bot.)
   A plant, whether recent or fossil, which resembles a seaweed.
   See Fucoid, a.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fucoid \Fu"coid\, a. [Fucus + -oid.] (Bot.)
   (a) Properly, belonging to an order of alga: (Fucoide[ae])
       which are blackish in color, and produce o["o]spores
       which are not fertilized until they have escaped from the
       conceptacle. The common rockweeds and the gulfweed
       (Sargassum) are fucoid in character.
   (b) In a vague sense, resembling seaweeds, or of the nature
       of seaweeds.
       [1913 Webster]

WordNet (r) 3.0 (2006):

fucoid
    n 1: a fossilized cast or impression of algae of the order
         Fucales
    2: any of various algae of the family Fucaceae [syn: fucoid,
       fucoid algae]