Good luck!
1. a wish of good luck to someone. Mary: I have my recital tonight. Jane: I know you'll do well. Good luck! Sally: I hear you're leaving for your new job tomorrow morning. Bob: That's right. Sally: Well, good luck!
2. You will certainly need luck, but it probably will not work. (Sarcastic.) Bill: I'm going to try to get this tax bill lowered. Sue: Good luck! Bill: I'm sure I can get this cheaper at another store. Clerk: Good luck!