“+ noun
Etymology: Medieval Latin or New Latin irrationalitas, from Latin irrationalis irrational + -itas -ity — more at irrational
1. : the quality or state of being irrational: as
a. : lack of being endowed with reason
b. : lack of accordance with reason : unreasonableness , foolishness
2. : something that is irrational : absurdity
3. : inequality of dispersion of different colors in refraction spectra (as between crown and flint glass)