WordWeb Online

1. Deviating from normal expectations; somewhat odd, strange, or abnormal
   "these days large families are atypical"; "atypical clinical findings";
   - irregular
    
2. Not representative of a group, class, or type
   "a class of atypical mosses"; "atypical behaviour is not the accepted type of response that we expect from children";
   - untypical, atypic

See also: abnormal, typicality, uncharacteristic, unnatural, unrepresentative

Encyclopedia: Atypical