Kelp \Kelp\ (k[e^]lp), n. [Formerly kilpe; of unknown origin.] 1. The calcined ashes of seaweed, -- formerly much used in the manufacture of glass, now used in the manufacture of iodine. [1913 Webster] 2. (Bot.) Any large blackish seaweed. [1913 Webster] Note: {Laminaria} is the common kelp of Great Britain; {Macrocystis pyrifera} and {Nereocystis Lutkeana} are the great kelps of the Pacific Ocean. [1913 Webster] {Kelp crab} (Zool.), a California spider crab ({Epialtus productus}), found among seaweeds, which it resembles in color. {Kelp salmon} (Zool.), a serranoid food fish ({Serranus clathratus}) of California. See {Cabrilla}. [1913 Webster]