A third of tri- is a prefix that means 'THREE'. It is derived from the Greek word 'trias' which means 'THREEFOLD'. The prefix is used to describe something that is composed of THREE parts or is divided into THREE parts. The crossword solutions for this term are MONO (4 letters) and UNI (3 letters). MONO means 'ONE' and UNI means 'ONE or single'. Therefore, these two words together represent the meaning of 'a third of tri-', which is 'THREE'.