Something which exerts a controlling or dominating influence.

In extended use: that which rules, governs, or has supremacy; a ruling power or principle. Chiefly literary. Obsolete.

A ruling or governing power; spec. human reason. Also: the supreme power in the universe. Cf. hegemon, n.

figurative. Applied to some influence or agency of enormous power. Sometimes prefixed as a title to names of personified qualities, in imitation of…