1. In dentistry, a dove-tailed or similarly shaped projection of a cavity prepared in a tooth into a surface perpendicular to the main part of the cavity for the purpose of preventing displacement of the restoration (filling) by the force of mastication.
4. A prefix used before father, mother, brother, sister, son, daughter, child, etc, to indicate that the person thus spoken of is not a blood relative, but is a relative by the marriage of a parent; as, a stepmother to X is the wife of the father of X, married by him after the death of the mother of X. See Stepchild, Stepdaughter, Stepson, etc.