You can use the noun transgressor for anyone who violates a rule or oversteps a boundary. You are being a transgressor, for example, when you bring your barking dog into the library.

A car thief is one kind of transgressor, a person who is actually breaking the law. Another kind of transgressor is someone who betrays an agreement or an unstated rule of behavior, like not wearing full clown makeup to a non-circus-related job interview. The word transgressionem is at the root of transgressor, and it means "a transgression of the law" in Late Latin or "a going over" in classical Latin.

Definitions of transgressor

n someone who transgresses; someone who violates a law or command

“the way of transgressors is hard”
Type of:
offender, wrongdoer
a person who transgresses moral or civil law

Sign up, it's free!

Whether you're a student, an educator, or a lifelong learner, can put you on the path to systematic vocabulary improvement.