hold something in—
1. (of an animal) control or restrain:
- Your horse is trying to go too fast; you must hold him in.
2. control one’s emotions:
- It was impossible for the children to hold in their laughter any longer.
keep something in—
1. retain smth. as part of a writing, performance, etc.:
- But that’s the best joke in the play, let’s keep it in!
2. = hold something in 2:
- Jim was able to keep his anger in and avoid a fight.
3. keep a supply of smth.:
- I always keep some good wine in for unexpected guests.