Source : Webster's Revised Unabridged Dictionary (1913)

Tattoo \Tat*too"\, v. t. [imp. & p. p. {Tattooed}; p. pr. & vb.
   n. {Tattooing}.] [Of Polynesian origin; cf. New Zealand ta to
   tattoo, tatu puncturation (in Otaheite).]
   To color, as the flesh, by pricking in coloring matter, so as
   to form marks or figures which can not be washed out.

Tattoo \Tat*too"\, n.; pl. {Tattoos}.
   An indelible mark or figure made by puncturing the skin and
   introducing some pigment into the punctures; -- a mode of
   ornamentation practiced by various barbarous races, both in
   ancient and modern times, and also by some among civilized
   nations, especially by sailors.

Tattoo \Tat*too"\, n. [Earlier taptoo, D. taptoe; tap a tap,
   faucet + toe to, shut (i. e., the taps, or drinking houses,
   shut from the soldiers).] (Mil.)
   A beat of drum, or sound of a trumpet or bugle, at night,
   giving notice to soldiers to retreat, or to repair to their
   quarters in garrison, or to their tents in camp.

   {The Devil's tattoo}. See under {Devil}.

Source : WordNet®

tattoo
     n 1: a drumbeat or bugle call that signals the military to return
          to their quarters
     2: a design on the skin made by tattooing
     3: the practice of making a design on the skin by pricking and
        staining
     v : stain (skin) with indelible color