Abstract concepts are ideas or concepts that cannot be touched, seen, heard, tasted or smelled. It is the intangible and complex nature of these concepts that make them difficult to define or express. A synonym for abstract concept could be an idea or a thought, a notion or a perspective, a belief or a philosophy, a theory or a hypothesis. Some other synonyms for abstract concepts include concepts, abstractions, constructs, or mental constructs. Other options may include ideals, values, principles, or standards. It is important to note that the type of synonym one chooses may depend on the context and the nature of the abstract concept under consideration.