mortar

(noun) a muzzle-loading high-angle gun with a short barrel that fires shells at high elevations for a short range. Synonyms: howitzer, trench mortar.

(noun) used as a bond in masonry or for covering a wall.

(noun) a bowl-shaped vessel in which substances can be ground and mixed with a pestle.

(verb) plaster with mortar. Example: "Mortar the wall."