catch up on someone—
1. overtake and overcome a person:
- The police caught up on the men just as they entered a dark archway.
2. have a marked effect on smb.:
- I think his past is beginning to catch up on him.
3. (coll.) learn the news of a person:
- I’ve had a visit from my friend John, and it was nice to catch up on him.
catch up with someone—
1. get level with a person when one has been left behind:
- Walk on ahead of me. I’ll catch up with you.
2. = catch up on someone 2:
- Jet lag caught up with Joe and he slept for fourteen hours.
3. reach the same stage as smb. after lagging behind:
- He’s working hard to catch up with the others.
4. make a person accountable for past deeds:
- Gronevelt felt that the FBI would catch up with them sooner or later.
5. (coll.) meet with smb. for a casual chat:
- “And what have you been up to?” “Nothing much. Catching up with a few people here.”