«وهو علم يعرف به إيراد المعنى الواحد بطرق مختلفة في وضوح الدلالة عليه»
It is the discipline through which one learns to express a single intended meaning by different methods that vary in the clarity of their indication.
One meaning (المعنى الواحد) is the underlying purpose that can be conveyed through several rhetorical forms. Different methods (طرق مختلفة) does not mean arbitrarily exchanging synonyms; the route by which the audience reaches the meaning may change.
The key phrase is clarity of indication (وضوح الدلالة). Some meanings are directly expressed, while others are reached through resemblance, contextual evidence or an associated implication. Those distinctions ground the study of simile, metaphor and kināyah.