helmetn.[OF. helmet, a dim of helme, F. heaume; of Teutonic origin; cf. G. helm, akin to AS. & OS. helm, D. helm, helmet, Icel. hjlmr, 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. arman protection. 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. (Chem.) That which resembles a helmet in form, position, etc.()Helmet beetle (Zol.), a leaf-eating beetle of the family Chrysomelid, having a short, broad, and flattened body. Many species are known. -- Helmet shell (Zol.), 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 (Zol.), an African wood shrike of the genus Prionodon, having a large crest.()