A curse (also called an imprecation, malediction, execration, malison, anathema, or commination) is any expressed wish that some form of adversity or misfortune will befall or attach to some other entity: one or more persons, a place, or an object. In particular, "curse" may refer to such a wish or pronouncement made effective by a supernatural or spiritual power, such as a god or gods, a spirit, or a natural force, or else as a kind of spell by magic or witchcraft; in the latter sense, a curse can also be called a hex or a jinx. In many belief systems, the curse itself (or accompanying ritual) is considered to have some causative force in the result. To reverse or eliminate a curse is sometimes called "removal" or "breaking", and is often believed to require elaborate rituals or prayers. The study of the forms of curses comprise a significant proportion of the study of both folk religion and folklore. The deliberate attempt to levy curses is often part of the practice of magic. In Hindu culture the Sage or Rishi is believed to have the power to bless and curse. Examples include the curse placed by Rishi Bhrigu on king Nahusha and the one placed by Rishi Devala. Special names for specific types of curses can be found in various cultures: Tecumsehs curse was reputed to cause the deaths in office of Presidents of the United States elected in years divisible by 20, beginning in 1840. This alleged curse appears to have fallen dormant, since Ronald Reagan, (elected in 1980) survived an assassination attempt and George W. Bush (elected in 2000) survived his eight-year presidency.