IPA: /ˈriː.zən.ə.blnəs/
KK: /ˈrizənəblnəs/
The quality of being fair, sensible, and logical in decisions or actions.
The reasonableness of her request made it easy for the manager to approve it.
Reasonableness → It is formed from "reason" (from Latin *ratio*, meaning a calculation or reasoning) and "-able" (meaning capable of) and "-ness" (meaning the state of). The word "reasonableness" refers to the state of being capable of reasoning or having sound judgment.
Think of 'reason' as the ability to think logically, and when you add '-able' (capable of) and '-ness' (the state of), it helps you remember that 'reasonableness' means the state of being capable of sound reasoning.