The term 'single undivided entity' can be summed up as a UNIT that is not divided or separated into parts. The crossword solution for this term is UNIT, which is a four letter word. A UNIT is a single thing, object, or individual that is not divided into parts. It is often used to refer to a group of people or things that are considered together as one. UNIT can also refer to a single item or element in a larger system.