A small protuberance is a raised area on a surface that is usually round or pointed. The term can be broken down into three parts: KNURL (5 letters), NUB (3 letters), and knop (4 letters). KNURL is a small, raised area on a surface that is usually round or pointed. NUB is a small lump or bump on a surface. Knop is a small knob or protuberance on a surface. All three terms refer to a small protuberance on a surface.