Irony
Following are examples of irony in the story:
The word lottery suggests that the villagers are going to draw for a prize.
The sunny day suggests that a happy event is about to take place.
When Old Man Warner hears that the north village is considering ending the lottery, he says, "Next thing you know, they'll be wanting to go back to living in caves." (The lottery is as savage and barbaric a ritual as any practiced by cave dwellers.)