line [L, linea] , 1. a connection between two points. 2. a stripe, streak, or narrow ridge, often imaginary, that serves to connect reference points or to separate various parts of the body, as the hairline or nipple line. 3. a black absorption line in a continuous spectrum passing through a medium. 4. an accretion line in the enamel of a tooth marking successive layers of calcification. 5. a catheter or wire that may be inserted in a vein, such as in an IV line. 6. the baseline of an electrocardiogram when neither positive nor negative potentials are recorded. 7. line of sight. Also called linea. See also Frankfurt horizontal plane.
