IPA: /ɪnˈsɛstəwəsli/
KK: /ɪnˈsɛstəˌwəsli/
In a way that involves sexual relations between closely related individuals, often considered taboo or illegal.
The story depicted the characters living in an incestuously close-knit community.
Incestuously → It is formed from "incestus" (from Latin, meaning unchaste or immoral) and the suffix "-ous" (meaning full of or characterized by). The word "incestuously" describes behavior that is characterized by incest or sexual relations between closely related individuals.
Think of 'unchaste' ('incestus') to remember that 'incestuously' refers to behavior that is full of such immoral relations.