The definition presupposes language that fits the requirements of the situation. Audience, setting, and purpose influence which expression is suitable.
When introducing the meaning of generosity to a beginner, the explicit explanation “Generosity is freely giving to others” is appropriate. In praising a generous person, “No petitioner leaves his door empty-handed” may be more evocative.
The disciplines are related but distinct: matching discourse to the situation is a central concern of ʿIlm al-Maʿānī; bayān studies different routes through which a fitting utterance communicates its target meaning, including differences of explicitness and inferential clarity.