Well-defined is a term commonly used to describe something that is clearly outlined and easily identifiable. However, there are several synonyms that can be used in place of this commonly used term. Some possible alternatives include terms such as distinct, clear-cut, sharply defined, precise, and explicit. Each of these options can be used to convey a similar meaning to "well-defined," but with slightly different connotations. For example, "distinct" may suggest a greater separation or differentiation than "well-defined," while "explicit" may connote more explicitness or specificity. Ultimately, the most appropriate synonym will depend on the context and intended meaning of the sentence or phrase in question.