The crossword solution for the term MINOR BUT NECESSARY PART is COG, which is a three-letter word. A COG is a small wheel or tooth on a gear that meshes with other cogs to form a larger gear system. It is an important part of a machine, as it helps to transfer power from one part of the machine to another. Cogs are used in many different types of machines, from bicycles to cars to industrial machinery. They are essential components of any machine, as they help to ensure that the machine runs smoothly and efficiently.