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.

Source: Webster's Revised Unabridged Dictionary (1913)