The term 'fall in' can be described by three crossword solutions: COLLAPSE (8 letters), CAVE (4 letters), and JOIN (4 letters). COLLAPSE is a verb meaning to suddenly fall down or give way, often due to external pressure or force. CAVE is a noun referring to a large, naturally-formed underground chamber or series of chambers. JOIN is a verb meaning to come together or unite, often with the purpose of forming a larger group or organization.