1. To experience a lot of mental, emotional, or physical strain or tension. Now, don't stress out, but the boss has some things he wants you to change in the project. I can't believe he's stressing out about something so trivial.

2. To cause someone to experience a lot of mental, emotional, or physical strain or tension. This term paper has been really stressing me out—I just don't know what to write for it! Try not to stress your employees out, as it can affect both their productivity and, in turn, your revenue potential.