The degree to which a thing is deadly. / The quality of being deadly. / Tedium, or the quality of being boring

plural of deadliness

(obsolete) Fatally, mortally. / In a way which suggests death. / Extremely, incredibly.

(obsolete, rare) Subject to death; mortal. / Causing death; lethal. / Aiming or willing to destroy; implacable; desperately hostile. / Very accurate (of aiming with a bow, firearm, etc.).

plural of deadly sin

The plant Atropa belladonna, a perennial shrub of the nightshade family that contains high concentrations of the alkaloid atropine which can be deadly if taken in excess.

Any of the seven deadly sins: anger, greed/avarice, envy, gluttony, lust, pride, and sloth.

(military) In nuclear weapons strategy: encouraging deterrence by guaranteeing an immediate, automatic, and overwhelming response to an attack, even if the command-and-control infrastructure has been damaged by the enemy's first strike.

(computing) deadlock

plural of deadly nightshade