(uncountable) A mixture of lime or cement, sand and water used for bonding building blocks.

(countable) A hollow vessel used to pound, crush, rub, grind or mix ingredients with a pestle.

(countable, military, historical) A short, heavy, large-bore cannon designed for indirect fire at very steep trajectories.

(countable, military) A relatively lightweight, often portable indirect fire weapon which transmits recoil to a base plate and is designed to lob explosive shells at very steep trajectories.

(countable) In paper milling, a trough in which material is hammered.

(transitive) To use mortar or plaster to join two things together.

(transitive) To pound in a mortar.

To fire a mortar (weapon).

To attack (someone or something) using a mortar (weapon).