mortar (n.1) Look up mortar at Dictionary.com
"mixture of cement," late 13c., from Old French mortier "builder's mortar, plaster; bowl for mixing" (13c.), from Latin mortarium "mortar," also "crushed drugs," probably the same word as mortarium "bowl for mixing or pounding" (see mortar (n.2)). Dutch mortel, German Mörtel are from Latin or French.
mortar (n.2) Look up mortar at Dictionary.com
"bowl for pounding," c.1300, from Old French mortier "bowl; builder's mortar," from Latin mortarium "bowl for mixing or pounding," also "material prepared in it," of unknown origin and impossible now to determine which sense was original (Watkins says probably from PIE root *mer- "to rub away, harm;" see morbid). Late Old English had mortere, from the same Latin source, which might also be a source of the modern word. German Mörser also is from Latin.
mortar (n.3) Look up mortar at Dictionary.com
"short cannon," 1550s, originally mortar-piece, from Middle French mortier "short cannon," in Old French, "bowl for mixing or pounding" (see mortar (n.2)). So called for its shape.