Sinful/ˈsɪnfl/ Definition 1 of 2Pro Tip 1/3Religious Origin In many religions, 'sinful' refers to actions violating divine laws. Lying is considered sinful. Pro Tip 2/3Cultural Variance 'Sinful' can imply different actions are wrong in various cultures. In some cultures, skipping the Sabbath is sinful. Pro Tip 3/3Moral Severity Using 'sinful' can suggest a serious moral wrongdoing. The politician's corrupt practices were seen as sinful.