Source : Webster's Revised Unabridged Dictionary (1913)

Grenade \Gre*nade"\, n. [F. grenade a pomegranate, a grenade, or
   Sp. granada; orig., filled with seeds. So called from the
   resemblance of its shape to a pomegranate. See {Carnet},
   {Grain} a kernel, and cf. {Pomegranate}.] (Min.)
   A hollow ball or shell of iron filled with powder of other
   explosive, ignited by means of a fuse, and thrown from the
   hand among enemies.

   {Hand grenade}.
   (a) A small grenade of iron or glass, usually about two and a
       half inches in diameter, to be thrown from the hand into
       the head of a sap, trenches, covered way, or upon
       besiegers mounting a breach.
   (b) A portable fire extinguisher consisting of a glass bottle
       containing water and gas. It is thrown into the flames.
       Called also {fire grenade}.

   {Rampart grenades}, grenades of various sizes, which, when
      used, are rolled over the pararapet in a trough.

Source : WordNet®

hand grenade
     n : a grenade designed to be thrown by hand