This verb describes the loss of feeling or sensitivity, whether physical or moral. In classical usage it could mean to cease grieving or to become despondent. The NT usage emphasizes moral desensitization—becoming callous or hardened beyond the reach of conscience. Ephesians 4:19 uses the perfect participle to describe those who 'having become callous, have given themselves over to sensuality.' The perfect tense indicates a settled state: they have deadened their moral sensitivity and now remain in that condition. Like skin that develops calluses from repeated friction, the conscience can lose responsiveness through repeated violation.