1. Fig. to stay up late waiting for someone to arrive or something to happen.

1. I’ll be home late. Don’t wait up for me.

2. We waited up for L the coming of the new year, and then we went to bed.

2. Fig. to wait for someone or something to catch up.

1. Hey! Don’t go so fast. Wait up for me.

2. Wait (Hold) up! You’re going too fast.