The term IT MAY BE STOLEN ON A DIAMOND can be solved by the four letter word BASE. BASE is a term used to describe the lowest part of something, such as the bottom of a structure or the foundation of a building. It can also refer to the starting point of a process or activity. In the context of a diamond, BASE refers to the part of the diamond that is closest to the setting and is not visible when the diamond is viewed from the top. This part of the diamond is vulnerable to theft, hence the phrase 'it may be stolen on a diamond'.