Famous Diamond is a term used to describe some of the most well-known and valuable diamonds in the world. Neil is a 4 letter word referring to the Neil Lane diamond, a 20 carat diamond that was given to actress Katherine Heigl as an engagement ring. HOPE is a 4 letter word referring to the HOPE Diamond, a 45.52 carat diamond that is currently on display at the Smithsonian Institution in Washington D.C. Kohinoor is an 8 letter word referring to the Kohinoor Diamond, a 105 carat diamond that is part of the British Crown Jewels.