fall out is a verb meaning "have a breach in relations". It carries 5 recorded senses.
come off
“His hair and teeth fell out”
leave (a barracks) in order to take a place in a military formation, or leave a military formation
“the soldiers fell out”
Definitions, synonyms and semantic relations for fall out come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.