Source : Webster's Revised Unabridged Dictionary (1913)

Alga \Al"ga\, n.; pl. {Alg[ae]}. [L., seaweed.] (Bot.)
   A kind of seaweed; pl. the class of cellular cryptogamic
   plants which includes the black, red, and green seaweeds, as
   kelp, dulse, sea lettuce, also marine and fresh water
   conferv[ae], etc.

Source : WordNet®

alga
     n : primitive chlorophyll-containing mainly aquatic eukaryotic
         organisms lacking true stems and roots and leaves [syn: {algae}]