ultima ratio

Noun

 * 1)  legal philosophy under which penal redress to crime should only be used as a measure of last resort

Etymology
, from the phrase that  had inscribed on the cannons made in 1650, and the similar one,, put by  on cannons after 1742, both almost certainly inspired by Spanish dramatist, poet, and writer , who, in one of his works of comedy, defined artillery as.

Noun

 * 1)  last resort