%incesttuou%

a. [ L. incestuosus: cf. F. incestueux. ] 1. Guilty of incest; involving, or pertaining to, incest; as, an incestuous person or connection. Shak. [ 1913 Webster ]

Ere you reach to this incestuous love,
You must divine and human rights remove. Dryden.

2. resembling incest; between people or groups so closely related as to make such activity improper or unethical; as, an incestuous coziness between the management of the company and its union; an incestuous relationship between the salesman and the purchasing manager. [ PJC ]

-- In*cest"tu*ous*ly, adv. -- In*cest"tu*ous*ness, n. [ 1913 Webster ]