Meaning of knuckle up | Babel Free

Definitions

1. To clench one's fist(s) as though in preparation for a fight.
   informal
2. To approach a problem aggressively.
   broadly, informal
3. To strike or fight.
   slang

Examples

“With a resolve to get his son away from these monsters, Isaac knuckled up and mean-mugged his opponent.”

“Tony stumbled a little and when he found his balance, he knuckled up and sent a jab toward Will's neck.”

CEFR level