You might still have terrifying dreams about the bully who harassed you on the playground in second grade. A bully is someone who intimidates people, usually those who are weaker or smaller.
The classic example of a bully is a mean kid in a schoolyard who hassles or beats up younger students. While a child or a teenager can be a bully, so is anyone who uses power or strength to scare or harm other people. The word bully has gone through a mysterious evolution, from the 1530s when it meant "sweetheart," through the 17th century's meanings of "fine fellow," then "blusterer," and finally "harasser of the weak."