adj.
- based on or in accordance with reason or logic.
- able to think sensibly or logically.
- having the capacity to reason.
- Mathematics (of a number, quantity, or expression) expressible, or containing quantities which are expressible, as a ratio of whole numbers.
Derivative
- rationality n.
- rationally adv.
Etymology
ME: from L. rationalis, from ratio(n-) (see ratio).