The term 'Geometer' is derived from the Greek words 'geo' meaning 'EARTH' and 'metron' meaning 'MEASURE'. It is used to describe a person who studies geometry, which is the branch of mathematics that deals with shapes, sizes, and relative positions of figures and with properties of space. Euclid, a 6-letter word, is one of the most famous geometers in history. He was an ancient Greek mathematician who wrote the Elements, a collection of 13 books on geometry, which is still used today as a standard textbook for teaching geometry.