1. Come on, Sam, we don’t have all day. Hurry up! Shake a leg!
2. I asked you ten minutes ago to stop playing and clean up this mess. We have to go in five minutes. You kids had better shake a leg.

Synonyms: Step on it!; Get a move on! Antonyms: hold (one’s) horses; keep (one’s) shirt onThe expression is never used in the past tense form “shook,” but it can be used in the future tense.