1) The word was used of a nobleman convicted of an act seriously dishonourable, such as *treason. The punishment was usually death and the forfeiture of all lands and estates, leaving descendants without inheritance.
Cf. previous
2) [atteint]. A hit, blow or strike. The term was used in jousting to signify a hit scored by one knight on another. When jousting in a friendly spirit, points were scored in various ways, e.g. by an attaint, by breaking a lance.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.