WordWeb Online

1. Liable to sudden unpredictable change
   "erratic behaviour";
   - fickle, mercurial, quicksilver
    
2. Having no fixed course
   "an erratic comet";
   - planetary, wandering
    
3. Likely to perform unpredictably
   "erratic winds are the bane of a sailor";
   - temperamental

1. (geology) a boulder of rock that differs from the surrounding bedrock because it has been transported by a glacier

Derived forms: erratics

See also: changeable, changeful, flakey [informal], flaky [informal], undependable, unreliable, unsettled

Encyclopedia: Erratic