\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.