Illegitimate means not following established rules, laws, or accepted standards. When something is illegitimate, it lacks proper authority or official recognition. A government that seizes power through force rather than fair elections is considered illegitimate because it didn't come to power the right way. An illegitimate business might operate without the required licenses or permits.

In everyday situations, you might hear someone call an excuse illegitimate when it's clearly made up or doesn't follow reasonable standards. If a student claims their homework disappeared because aliens took it, a teacher might reject that as an illegitimate excuse, one that doesn't meet basic standards of believability or honesty.

The word also has a historical meaning related to children born to parents who weren't married. In centuries past, societies treated such children unfairly, denying them inheritance rights or social standing. This usage appears in older books and historical documents, but today many people avoid using it about children because it can be hurtful and unfair.

The opposite of illegitimate is legitimate, meaning proper, legal, or genuine. A legitimate concern is one that makes sense and deserves attention. A legitimate ruler has proper authority. Understanding what makes something legitimate helps you recognize when rules and fairness actually matter.