1. Literally, to have hair that has lightened to a grayish color, typically due to aging. I'm only 30—how do I have gray hair already?

2. By extension, to experience negative or undesired physical effects (such as having gray hair) from being exceedingly worried, stressed, or upset by or about something or someone. I'm going to have gray hair after being around these screaming kids all day long. I'm going to have gray hair from my teenage daughter and all her wild behavior. I'm going to have gray hair from dealing with this stupid car breaking down all the time!