fall-in

(verb) break down, literally or metaphorically. Synonyms: collapse, fall in, cave in, give, give way, break, founder. Examples: "The wall collapsed." "The business collapsed." "The dam broke." "The roof collapsed." "The wall gave in." "The roof finally gave under the weight of the ice."

(verb) to take one's place in a military formation or line. Synonyms: fall in. Example: "Troops fall in!."

(verb) become part of; become a member of a group or organization. Synonyms: join, fall in, get together. Example: "He joined the communist party as a young man."