Source : Webster's Revised Unabridged Dictionary (1913)

Sagitta \Sa*git"ta\, n. [L., an arrow.]
   1. (Astron.) A small constellation north of Aquila; the
      Arrow.

   2. (Arch.) The keystone of an arch. [R.] --Gwilt.

   3. (Geom.) The distance from a point in a curve to the chord;
      also, the versed sine of an arc; -- so called from its
      resemblance to an arrow resting on the bow and string.
      [Obs.]

   4. (Anat.) The larger of the two otoliths, or ear bones,
      found in most fishes.

   5. (Zo["o]l.) A genus of transparent, free-swimming marine
      worms having lateral and caudal fins, and capable of
      swimming rapidly. It is the type of the class
      Ch[ae]tognatha.

Source : WordNet®

Sagitta
     n 1: a small constellation in the northern hemisphere between
          Cygnus and Aquila and crossed by the Milky Way
     2: any arrowworm of the genus Sagitta