The term 'diamond surface' refers to the outermost layer of a diamond, which is composed of many small facets. The crossword solutions for this term are 'FACET' (5 letters), 'lil' (3 letters), and 'neil' (4 letters). FACET is a term used to describe the individual flat surfaces that make up the diamond's exterior. Lil is an abbreviation for luster, which is the amount of light reflected off the diamond's surface. Neil is an abbreviation for polish, which is the degree of smoothness on the diamond's surface.