means A workable paste (typically cement, sand, and water) used to bond bricks or stones together, or—separately—a short stubby cannon that fires shells in a high arc; also the heavy bowl in which substances are crushed with a pestle.

from From Latin 'mortarium,' which named both the crushing bowl and the substance pounded within it—the bowl giving its name to the stuff. The word arrived in English through Old French 'mortier.' The weapon picked up the name later because early mortars were squat, thick-walled, and bowl-like, resembling the grinding vessel they were named for. So the bowl, the building paste, and the cannon all trace back to that single Latin pot.