1 The act of adding or accretion. Growth by apposition is characteristic of many tis- sues in the body by which nutritive matter from the blood is transformed on the surface of an organ into a solid unorganized substance. 2 The act of put- ting things in juxtaposition or side by side. To lose a pair of apposed teeth is to lose teeth that are next to each other. Also known as juxtaposition.