The term 'keep separate' can be expressed in two different ways in a crossword puzzle. The first is 'ISOLATE' which is seven letters long and the second is 'INSULATE' which is eight letters long. ISOLATE means to keep apart or to separate, while INSULATE means to protect from outside influences or to shield from contact with others. Both words are used to describe the concept of keeping something or someone apart from other things or people.