task, job, chore, stint, assignment
These nouns denote a piece of work that one must do.
1) A task is a well-defined responsibility that is usually imposed by another and that may be burdensome: I stayed at work late to finish the task at hand.
2) Job often suggests a specific short-term undertaking: "did little jobs about the house with skill" (W.H. Auden).
3) Chore generally denotes a minor, routine, or odd job: The farmer's morning chores included milking the cows.
4) Stint refers to a person's prescribed share of work: Her stint as a lifeguard usually consumes three hours a day.
5) Assignment generally denotes a task allotted by a person in authority: His homework assignment involved writing an essay.