The Collaborative International Dictionary of English v.0.48:

Tubercle \Tu"ber*cle\, n. [L. tuberculum, dim. of tuber: cf. F.
   tubercule, OF. also tubercle. See Tuber.]
   [1913 Webster]
   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.
      [1913 Webster]

   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.
      [1913 Webster]

   Tubercle bacillus (Med.), a minute vegetable organism
      (Mycobacterium tuberculosis, formerly Bacillus
      tuberculosis, and also called Koch's bacillus)
      discovered by Koch, a German physician, in the sputum of
      consumptive patients and in tuberculous tissue. It is the
      causative agent of tuberculosis.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Tuberculosis \Tu*ber`cu*lo"sis\, n. [NL. See Tubercle.] (Med.)
   A constitutional disease caused by infection with
   Mycobacterium tuberculosis (also called the Tubercle
   bacillus), characterized by the production of tubercles in
   the internal organs, and especially in the lungs, where it
   constitutes the most common variety of pulmonary phthisis
   (consumption). The Mycobacteria are slow-growing and without
   cell walls, and are thus not affected by the beta-lactam
   antibiotics; treatment is difficult, usually requiring
   simultaneous administration of multiple antibiotics to effect
   a cure. Prior to availability of antibiotic treatment, the
   cure required extensive rest, for which special sanatoriums
   were constructed.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Mycobacterium tuberculosis
    n 1: cause of tuberculosis [syn: tubercle bacillus,
         Mycobacterium tuberculosis]