Eating the last cookie without sharing? That's just mean. But if you stole that cookie and then lied about it, that would be morally wrong, or unethical.

The prefix un- means "not," so something or someone who's unethical is literally "not ethical." In other words, that someone is lacking principles or morals. Because being unethical involves going against social or professional expectations of what's right, it's a word that's often used to describe bad behavior or immoral conduct. So like the great philosophers, you can decide if Cookie Monster has an ethics problem — or just bad eating habits.

Definitions of unethical

adj not conforming to approved standards of social or professional behavior

unethical business practices”
contrary to conscience or morality or law
conforming to accepted standards of social or professional behavior
in conformance with justice or law or morality
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