WordWeb Online

1. Misbehave badly; act in a silly or improper way
   "The children acted up when they were not bored";
   - carry on
    
2. Make itself felt as a recurring pain
   "My arthritis is acting up again"

Derived forms: acts up, acted up, acting up

See also: act

Type of: ache, hurt, misbehave, misconduct, misdemean, smart

Encyclopedia: Act up