stolen
Taken without permission and not meant to be given back.
To steal something means to take it from someone without permission and without intending to give it back. When a person steals, they're taking something that belongs to someone else, whether it's a bike from a yard, money from a wallet, or answers copied from a classmate's homework.
The word stolen describes something that has been taken this way. A stolen bicycle is one that someone took without the owner's consent. A stolen idea means someone claimed credit for thoughts or work that really belonged to someone else.
Stealing isn't the same as borrowing. When you borrow something, you ask first and plan to return it. When you steal, you take it secretly and keep it. Even taking small things counts as stealing: pocketing candy from a store without paying, or “borrowing” your sister's favorite pen with no intention of ever giving it back.
People sometimes use “stolen” more loosely, like when a basketball player makes a steal by intercepting the other team's pass. Or when someone says their little brother “stole the show” at the school concert, meaning he unexpectedly became the center of attention. But these uses just borrow the word's suddenness and surprise, not its unfairness.