Source : Webster's Revised Unabridged Dictionary (1913)

Helmet \Hel"met\, n. [OF. helmet, a dim of helme, F. heaume; of
   Teutonic origin; cf. G. helm, akin to AS. & OS. helm, D.
   helm, helmet, Icel. hj[=a]lmr, Sw. hjelm, Dan. hielm, Goth.
   hilms; and prob. from the root of AS. helan to hide, to hele;
   cf. also Lith. szalmas, Russ. shleme, Skr. [,c]arman
   protection. [root]17. Cf. {Hele}, {Hell}, {Helm} a helmet.]
   1. (Armor) A defensive covering for the head. See {Casque},
      {Headpiece}, {Morion}, {Sallet}, and Illust. of {Beaver}.

   2. (Her.) The representation of a helmet over shields or
      coats of arms, denoting gradations of rank by
      modifications of form.

   3. A helmet-shaped hat, made of cork, felt, metal, or other
      suitable material, worn as part of the uniform of
      soldiers, firemen, etc., also worn in hot countries as a
      protection from the heat of the sun.

   4. That which resembles a helmet in form, position, etc.; as:
      (a) (Chem.) The upper part of a retort. --Boyle.
      (b) (Bot.) The hood-formed upper sepal or petal of some
          flowers, as of the monkshood or the snapdragon.
      (c) (Zo["o]l.) A naked shield or protuberance on the top
          or fore part of the head of a bird.

   {Helmet beetle} (Zo["o]l.), a leaf-eating beetle of the
      family {Chrysomelid[ae]}, having a short, broad, and
      flattened body. Many species are known.

   {Helmet shell} (Zo["o]l.), one of many species of tropical
      marine univalve shells belonging to {Cassis} and allied
      genera. Many of them are large and handsome; several are
      used for cutting as cameos, and hence are called {cameo
      shells}. See {King conch}.

   {Helmet shrike} (Zo["o]l.), an African wood shrike of the
      genus {Prionodon}, having a large crest.