Collins COBUILD Advanced Learner's English Dictionary - keep back

1. If you keep back part of something, you do not use or give away all of it, so that you still have some to use at a later time. Roughly chop the vegetables, and keep back a little to chop finely and serve as a garnish. = set aside, hold back PHRASAL VERB: V P n (not pron), also V n P 2. If you keep some information back, you do not tell all that you know about something. Neither of them is telling the whole truth. Invariably, they keep something back. PHRASAL VERB: V n P, also V P n (not pron)