Mortar is a mixture of sand, water, and cement (or lime) that hardens like stone. Bricklayers spread mortar between bricks or stones to hold them together permanently. When you look closely at a brick wall, those gray lines between the bricks are mortar. Ancient Romans used mortar to build structures like the Colosseum and aqueducts, many of which still stand today after 2,000 years.

The word also refers to a bowl-shaped tool used for grinding. A pharmacist might use a mortar and pestle (the grinding stick) to crush pills into powder. Cooks use them to grind spices like peppercorns or to mash garlic into paste. The mortar holds the ingredients while the pestle does the crushing work.

In military contexts, a mortar is a short cannon that shoots explosive shells high into the air so they drop down on targets. Unlike regular cannons that fire in a flat line, mortars lob their projectiles in a high arc, which is useful for reaching enemies behind walls or hills.