A barbarous word from the Latin præmoneri (to be forewarned). The words of the writ begin “Præmunire facias A.B.” - i.e. “Cause A.B. to be forewarned,” to appear before us to answer the contempt wherewith he stands charged. If A.B. refuses to do so, he loses all civil rights, and before the reign of Elizabeth might have been slain by anyone with impunity.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894