From Longman Dictionary of Contemporary Englishmortarmor‧tar /ˈmɔːtə $ ˈmɔːrtər/ noun 1 [uncountable]TBC a mixture of cement or lime, and sand and water, used in building for holding bricks or stones together2 [countable]PMW a heavy gun that fires bombs or shells in a high curve A cameraman was killed when his vehicle came under mortar fire. a mortar attack3 
[countable]DH a stone bowl in which substances are crushed with a pestle (=tool with a heavy round end) You’ll need a pestle and mortar to grind the spices. → bricks and mortar at brick1(2)
[countable]DH a stone bowl in which substances are crushed with a pestle (=tool with a heavy round end) You’ll need a pestle and mortar to grind the spices. → bricks and mortar at brick1(2)Examples from the Corpus
mortar• They used helicopters, airplanes and mortars.• On downtown streets, broken glass covered many sidewalks and fallen bricks and mortar dented cars.• Soldiers had parachuted across, but mortar fire had seen them off.• Most of the Brigade casualties so far have been caused mainly by mortar and shellfire and, of course, the constant sniping.• The following day we used proper plaster over the hardened mortar, but cellulose filler could also have been used.• Leese and I looked at each other as the mortars got closer.• The mortar team have started up again, sending their shells through the drizzle.mortar fire• Soldiers had parachuted across, but mortar fire had seen them off.• I gave no thought to this until heavy mortar fire began to hit extremely close.• Our firebase had been taking mortar fire from a wooded area some distance away.• A great crowd collected, not withstanding the concentration of the mortar fire; and yet there were no remembered casualties.• The mortar fire went on relentlessly, and showers of earth went up.• Their car came under mortar fire and they had to cross five military checkpoints.• Each time we came in there was mortar fire and plumes of smoke.• Around dawn they were hit with mortar fire.Origin mortar (1000-1100) Old French mortier, from Latin mortarium 