1 involving illegal sex between members of the same family 涉及乱伦的: an incestuous relationship 乱伦的关系

2 (used about a group of people and their relationships with each other) too close; not open to anyone outside the group （指一群人及他们之间的关系）过分亲密的，排外的，小圈子的: Life in a small community can be very incestuous. 小小区的生活有时是非常排外的。