roost / roōst/ • n. a place where birds regularly settle or congregate to rest at night, or where bats congregate to rest in the day. • v. [intr.] (of a bird or bat) settle or congregate for rest or sleep: migrating martins and swallows were settling to roost. PHRASES: come home to roost (of a scheme, etc.) recoil unfavorably upon the originator: ensuring that the liability does not come home to roost. rule the roost see rule.