definition of
fall in

[1] #1 fall in v. break down, literally or metaphorically; "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". wn

[2] #2 fall in v. to take one's place in a military formation or line; "Troops fall in!". wn

[3] #3 fall in v. become part of; become a member of a group or organization; "He joined the Communist Party as a young man". wn