Characterized by an excessively close or exclusive relationship within a group that resists outside influence; self-contained to the point of lacking diversity or impartiality.

The company's board was criticized for its incestuous structure, as all the members were long-time friends of the CEO.

Involving or relating to sexual intercourse between people who are too closely related to marry legally.

The court heard evidence about the man's incestuous relationship with his daughter.