The term 'Diamond Unit' is composed of three words: INNING (6 letters), CARAT (5 letters), and INIG (4 letters). Inning is a baseball term referring to one of the nine divisions of a game, while CARAT is a unit of measurement used to determine the weight of a diamond. INIG is an acronym for International Institute of Gemology, which is an organization that provides certification for diamonds. Together, these three words form the term 'Diamond Unit, ' which is a measure of the quality and value of a diamond.