Fully matured is a term used to describe something that has reached its peak development and is ready for use. In the context of a crossword puzzle, the terms RIPE (4 letters) and MELLOW (6 letters) can be used to describe fully matured. RIPE implies that something has reached its peak ripeness and is ready to be consumed, while MELLOW implies that something has been aged and has developed a smooth flavor. Together, these two words can be used to describe something that has reached its full potential.