1. The quality or state of being irrational; lack of reason or logic
The irrationality of his decision surprised everyone.
A irracionalidade da sua decisão surpreendeu a todos.
2. An irrational act, belief, or thought
Fear often leads to irrationality.
O medo frequentemente leva à irracionalidade.
3. In mathematics, a number that cannot be expressed as a ratio of two integers
The irrationality of pi has been proven mathematically.
A irracionalidade de pi foi comprovada matematicamente.