Which term expresses a quality of being intrinsically involved or essential?

The term that best expresses a quality of being intrinsically involved or essential is "inherent." This word is used to describe characteristics or attributes that are a fundamental and integral part of something. When something is inherent, it means that it cannot be separated from the entity it belongs to; it is essential to its nature.

In contrast, the other terms do not capture this intrinsic aspect. For instance, "indomitable" refers to something that cannot be subdued or overcome, which does not relate to essential qualities. "Inhibited" describes a state of being restrained or prevented from acting, while "indifferent" indicates a lack of interest or concern. Neither of these terms addresses the concept of being an essential part of something. Therefore, "inherent" is the most accurate descriptor for qualities that are naturally part of an entity.