Inlying is a fairly uncommon word which can mean something inherent or built-in. When looking for synonyms, one could use words such as underlying, inherent, intrinsic, essential, innate or inherent. These words all refer to something that is a fundamental part of something else. Underlying, for instance, refers to the foundation or basis of something, while intrinsic refers to qualities that something has by nature rather than through external factors. Essential denotes something that is necessary, while innate refers to something that is existing in a person or thing since birth or creation. Synonyms for inlying are useful for establishing an understanding of something's character.