|a.||1.||Guilty of incest; involving, or pertaining to, incest; as, an incestuous person or connection.|
Ere you reach to this incestuous love,
You must divine and human rights remove.
|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.|
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.