keep (something) back = keep something a secret
examples:
- Did you tell them all the truth or did you keep a few facts back?
- She tried to be calm and act as if everything was fine, but I knew she was keeping something back.
- You look very suspicious! Come on! What are you keeping back?
- He reported the accident to the police but kept back some information that proved that he was responsible for it.
- I would never keep back something from you. You know I always tell you everything.
- You can keep back the bad news about a patient 's health from the patient but you can 't keep it back from the patient 's family.
