fall out (Noun) — The radioactive particles that settle to the ground after a nuclear explosion.
fall out (Noun) — Any adverse and unwanted secondary effect. ex. "a strategy to contain the fallout from the accounting scandal"
fall out (Verb) — Have a breach in relations. ex. "We fell out over a trivial question"
fall out (Verb) — Be a logical consequence. ex. "the theorem falls out nicely"
fall out (Verb) — Come off. ex. "His hair and teeth fell out"
fall out (Verb) — Leave (a barracks) in order to take a place in a military formation, or leave a military formation. ex. "the soldiers fell out"
fall out (Verb) — (of an event) come to pass (in time, so that it is real and actual at some time). ex. "What is falling out?"