The term 'undivided whole' can be represented by the crossword solution UNIT, which is a four-letter word. A UNIT is a single, undivided entity that is not divided into parts. It is often used to refer to a single item or object, such as a single piece of furniture or a single UNIT of measurement. In mathematics, a UNIT is a number that is equal to one. In physics, a UNIT is a measure of a physical quantity, such as length, mass, or time. In philosophy, a UNIT is an indivisible entity that cannot be divided into smaller parts.