n. The act of interpenetrating; reciprocal or mutual penetration; the occupation of the same space by the parts of two bodies.n. In late medieval arch., from the end of the fifteenth century, the system of continuing moldings which meet each other independently past, the intersection, and generally of considering the identity of various architectural members as preserved after one has come to coincide partly with another or to be swallowed up in it, so that, for instance, the angles and edges of a square member which has become united with a member having a curved surface are shown on the curved surface as if projecting through it.