1. To become silent. Often said as an imperative. We all shushed up after the teacher slammed the book on his desk. Shush, you two! I'm trying to watch the movie! Would you please shush up?
2. To instruct or command someone to become silent. A noun or pronoun can be used between "shush" and "up" (if "up" is used). I had to shush the people behind me throughout the entire play. Would you please shush up your kids? They're bothering everyone! He had started rambling a bit, so I put my hand on his knee to shush him up.
3. To cause someone to cease making criticisms or negative remarks. A noun or pronoun can be used either before or after "up" (if "up" is used). The team's decisive victory in the Super Bowl will undoubtedly shush up those who though they would never make it to the playoffs, let alone win the thing. The new CEO has managed to shush his detractors after returning the company to profitability after just six months in the job.
See also: shush
in. to be quiet. Shush! I want to hear the weather.