(verb) to admit that something you said in the past was wrong
A: Canada is the biggest country in the world.
B: No it’s not, it’s Russia.
A: Russia? You idiot, it’s Canada!
B: Let’s check on the internet! They check.
A: Well, you’re right. Looks like I have to eat my words
After telling the student that he was going to fail the class, the professor ate his words when the student got 100% on the final exam.