E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A child-killer; from Herod the Great, who ordered the massacre of the babes in Bethlehem. (Matt. ii. 16.)
To out-herod Herod. To out-do in wickedness, violence, or rant, the worst of tyrants. Herod, who destroyed the babes of Bethlehem, was made (in the ancient mysteries) a ranting, roaring tyrant; the extravagance of his rant being the measure of his bloody-mindedness. (See PILATE.)
Oh, it offends me to the soul to hear a robustious, periwig-pated fellow tear a passion to tatters, to very rags, to split the ears of the groundlings . it out-herods Herod.Shakespeare: Hamlet, iii. 2.