1. To make many fast small movements up and down, or side to side: The ground and Jason’s house was shaking during the earthquake at night and he and his family almost fell out of their beds!
2. To move or to have parts of a person's body move in short, quick movements and in such a way as to lose control: Expecting her father to call about her mother's condition, Shanna's hand shook as she reached for the phone.

An important modification, change, or a series of changes in the way a company or other organization is run: There has been a major shake-up in Jim's company since profits have decreased so much.