This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

adj. Of, involving, or suggestive of incest.

adj. Having committed incest.

adj. Improperly intimate or interconnected: "Press-politics relations are notoriously incestuous” ( Boston Globe).

adj. Pertaining to or engaging in incest.

adj. Characterized by mutual relationships that are intimate and exclusive to the detriment of outsiders.

Guilty of incest: as, an incestuous person.

Involving the crime of incest: as, an incestuous connection.

adj. relating to or involving incest

adj. resembling incest as by excessive intimacy

"Fred Siegel, a historian at the conservative-leaning Manhattan Institute, has written of the "New Tammany Hall," which he describes as the incestuous alliance between public officials and labor."

incestuously   

adulterous    heterosexual    same-sex    illicit    indissoluble    morganatic    carnal    unhallowed    illegitimate    ill-assorted