intransitive verb
Etymology: warm (II) + up
1. : to engage in exercise or practice especially immediately before entering a game or contest in order to limber up the muscles, work up speed, or get in condition
the pitcher was warming up with an overhand delivery — Dan Polier
2. : to approach a state of or become characterized by violence, conflict, or danger
as the campaign warmed up … hired assassins had been brought in — H.H.Martin