The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]