The term PART OF REM is composed of two crossword solutions: EYE (3 letters) and RAPID (5 letters). The first solution, EYE, refers to the eyes being a part of the RAPID EYE Movement (REM) stage of sleep. During this stage, the eyes move rapidly in different directions while the body is still and relaxed. The second solution, RAPID, refers to the speed at which the eyes move during the REM stage. This stage of sleep is important for memory consolidation and learning.