This noun means habit or settled disposition, particularly one formed through practice. Hebrews 5:14 speaks of mature believers whose faculties are trained 'by reason of use' to discern good and evil. The term denotes the settled state produced by habitual practice, as opposed to temporary condition. Classical usage distinguished fixed habit from changeable state. The author emphasizes that spiritual discernment comes not from one-time learning but from habituated practice—moral muscles developed through repeated exercise of judgment.