The term 'Fit One Within Another' can be summarized by two crossword solutions: NESTED (6 letters) and NEST (4 letters). Nested means to place one object within another, such as a box inside a larger box. Nesting is often used to store items in an organized manner. The word NEST is a verb that means to settle or build a home in a particular place. It can also refer to a group of objects placed together in a way that resembles a bird's NEST.