Definition of petalism in US English:

petalism

noun

Ancient Greek History
  • The custom of temporary banishment (for five years) practised in ancient Syracuse, effected by writing the name of the person banished on an olive leaf (rather than on a potsherd, as in the ostracism of Athens).

Origin

Early 17th century; earliest use found in Thomas North (1535–?1603), translator. From French pétalisme or its etymon Hellenistic Greek πεταλισμός from ancient Greek πέταλον leaf + -ισμός.