Source : Webster's Revised Unabridged Dictionary (1913)

Tubercle \Tu"ber*cle\, n. [L. tuberculum, dim. of tuber: cf. F.
   tubercule, OF. also tubercle. See {Tuber}.]
   1. A small knoblike prominence or excrescence, whether
      natural or morbid; as, a tubercle on a plant; a tubercle
      on a bone; the tubercles appearing on the body in leprosy.

   2. (Med.) A small mass or aggregation of morbid matter;
      especially, the deposit which accompanies scrofula or
      phthisis. This is composed of a hard, grayish, or
      yellowish, translucent or opaque matter, which gradually
      softens, and excites suppuration in its vicinity. It is
      most frequently found in the lungs, causing consumption.

   {Tubercle bacillus} (Med.), a minute vegetable organism
      ({Bacillus tuberculosis}) discovered by Koch, a German
      physician, in the sputum of consumptive patients and in
      tuberculous tissue, and believed to be the exciting cause
      of tubercles and tuberculosis.