WordWeb Online

1. Characterized by iniquity; wicked because it is believed to be a sin
   "he said it was sinful to wear lipstick";
   - iniquitous, ungodly
    
2. Having committed unrighteous acts
   "a sinful person";
   - unholy, wicked
    
3. Far more than usual or expected
   - extraordinary, over-the-top

See also: immoderate, unrighteous, wicked

Encyclopedia: Sinful