Merriam-Webster Collegiate Dictionary - mortise

 I. noun  also mortice  Etymology: Middle English mortays, from Anglo-French mortais  Date: 15th century a hole, groove, or slot into or through which some other part of an arrangement of parts fits or passes; especially a cavity cut into a piece of material (as timber) to receive a tenon — see dovetail illustration  II. transitive verb  also mortice  (~d; also morticed; mortising; also morticing)  Date: 15th century  1. to join or fasten securely; specifically to join or fasten by a tenon and ~  2. to cut or make a ~ in