A chore is a duty or task you’re obligated to perform, often one that is unpleasant but necessary. Washing the dishes is a chore, and so is completing a homework assignment you aren’t excited about.
Sometimes a thing that you wanted to do can become a chore if it ceases to be fun or interesting. Maybe Napoleon felt that conquering nations had become a chore by the time he was defeated in the Battle of Waterloo. The noun chore dates from the 18th century, when there were fewer appliances and more household tasks that needed to be done.