As-Salamu 'Alaykum wa Rahmatullahi wa Barakatuh: The term reasonable is used in many ayat of Qur'an, such as, Al-Baqara, Chapter #2, Verse #180) Mohsin Khan interpretation, but is the term Reasonable actually defined in Shari'ah? We are told to act according to what is reasonable, but has the concept of reasonability been defined? Was-Salamu 'Alaykum wa Rahmatullahi wa Barakatuh.

AAWW

The exact Arabic context of (Reasonable) you refer to in your question is المعروف and it has various meanings in the Quran depending on the context and the passage itself.

In the Ayah you referred to, the word (reasonable) means just or fair. While in some other places in the Quran المعروف means what is permissible in Islam, obligatory matters, common sense,..etc