Rēa'son-a-ble-ness, n.
n. 1. The faculty of reason; rationality. [Rare.]
Sense 2. The quality of being reasonable; agreeableness to reason; that state or quality of a thing which reason supports or justifies; conformity to rational principles; moderation; as, the reasonableness of our wishes, demands, or expectations. “The reasonableness and excellency of charity.” Law.