Influenza (?), n. [It. influenza influence, an epidemic formerly attributed by astrologers to the influence of the heavenly bodies, influenza. See Influence.] (Med.) An epidemic viral infectious disease characterized by acute nasal catarrh, or by inflammation of the throat or the bronchi, and usually accompanied by fever and general weakness; also called grippe. It is caused by several forms of RNA virus which mutate readily and thereby render vaccines prepared against older forms ineffective, often requiring a new form of vaccine for each new outbreak.
[1913 Webster +PJC]