1.Definition: deviating from normal expectations; somewhat odd, strange, or abnormal

"These days large families are atypical", "Atypical clinical findings", "Atypical pneumonia"

Related Adjective(s):irregular

2.Definition: not representative of a group, class, or type

"A class of atypical mosses", "Atypical behavior is not the accepted type of response that we expect from children"

Related Adjective(s):atypic, untypical