The term 'One BERRY in a Cluster' can be solved by the word 'Acinus', which is a six-letter word. Acinus is a Latin word meaning 'BERRY' and is used to describe a small, rounded structure found in certain glands and organs. It is also used to refer to a cluster of cells or granules that are found in the acinar region of the pancreas. In botany, it is used to describe a single drupe or BERRY in a cluster of fruits.