(1):

(n.) The act of secreting; the process by which material is separated from the blood through the agency of the cells of the various glands and elaborated by the cells into new substances so as to form the various secretions, as the saliva, bile, and other digestive fluids. The process varies in the different glands, and hence are formed the various secretions.

(2):

(n.) Any substance or fluid secreted, or elaborated and emitted, as the gastric juice.

(3):

(n.) The act of secreting or concealing; as, the secretion of dutiable goods.