Source : Webster's Revised Unabridged Dictionary (1913)

Water scorpion \Wa"ter scor"pi*on\ (Zo["o]l.)
   See {Nepa}.

Scorpion \Scor"pi*on\, n. [F., fr. L. scorpio, scorpius, Gr. ?,
   perhaps akin to E. sharp.]
   1. (Zo["o]l.) Any one of numerous species of pulmonate
      arachnids of the order Scorpiones, having a suctorial
      mouth, large claw-bearing palpi, and a caudal sting.

   Note: Scorpions have a flattened body, and a long, slender
         post-abdomen formed of six movable segments, the last
         of which terminates in a curved venomous sting. The
         venom causes great pain, but is unattended either with
         redness or swelling, except in the axillary or inguinal
         glands, when an extremity is affected. It is seldom if
         ever destructive of life. Scorpions are found widely
         dispersed in the warm climates of both the Old and New
         Worlds.

   2. (Zo["o]l.) The pine or gray lizard ({Sceloporus
      undulatus}). [Local, U. S.]

   3. (Zo["o]l.) The scorpene.

   4. (Script.) A painful scourge.

            My father hath chastised you with whips, but I will
            chastise you with scorpions.          --1 Kings xii.
                                                  11.

   5. (Astron.) A sign and constellation. See {Scorpio}.

   6. (Antiq.) An ancient military engine for hurling stones and
      other missiles.

   {Book scorpion}. (Zo["o]l.) See under {Book}.

   {False scorpion}. (Zo["o]l.) See under {False}, and {Book
      scorpion}.

   {Scorpion bug}, or {Water scorpion} (Zo["o]l.) See {Nepa}.

   {Scorpion fly} (Zo["o]l.), a neuropterous insect of the genus
      {Panorpa}. See {Panorpid}.

   {Scorpion grass} (Bot.), a plant of the genus {Myosotis}. {M.
      palustris} is the forget-me-not.

   {Scorpion senna} (Bot.), a yellow-flowered leguminous shrub
      ({Coronilla Emerus}) having a slender joined pod, like a
      scorpion's tail. The leaves are said to yield a dye like
      indigo, and to be used sometimes to adulterate senna.

   {Scorpion shell} (Zo["o]l.), any shell of the genus
      Pteroceras. See {Pteroceras}.

   {Scorpion spiders}. (Zo["o]l.), any one of the Pedipalpi.

   {Scorpion's tail} (Bot.), any plant of the leguminous genus
      {Scorpiurus}, herbs with a circinately coiled pod; -- also
      called {caterpillar}.

   {Scorpion's thorn} (Bot.), a thorny leguminous plant
      ({Genista Scorpius}) of Southern Europe.

   {The Scorpion's Heart} (Astron.), the star Antares in the
      constellation Scorpio.

Source : WordNet®

water scorpion
     n : long-legged aquatic insect having the front legs fitted for
         seizing and holding prey and the abdomen extended by a
         long breathing tube