(1):

(n.) That which taints or corrupts morally; as, the infection of vicious principles.

(2):

(n.) Sympathetic communication of like qualities or emotions; influence.

(3):

(n.) Contamination by illegality, as in cases of contraband goods; implication.

(4):

(n.) The state of being infected; contamination by morbific particles; the result of infecting influence; a prevailing disease; epidemic.

(5):

(n.) That which infects, or causes the communicated disease; any effluvium, miasm, or pestilential matter by which an infectious disease is caused.

(6):

(n.) The act or process of infecting.