atypical

/ˈeɪˌtɪpɪkəl/

/eɪˈtɪpɪkəl/

Typical means what you would expect—a typical suburban town has lots of neat little houses and people. Atypical means outside of type—an atypical suburban town might be populated by zombies in damp caves.

Atypical is a synonym of "unusual," but it carries a more objective feel—scientific studies might mention atypical results, suggesting that there is a clear definition of what is typical and what is not. "Unusual" is more of a casual observation that one might make in a non-scientific context.

Definitions of atypical

1. adjective

   not representative of a group, class, or type
   “a group that is atypical of the target audience”

   “a class of atypical mosses”

   “atypical behavior is not the accepted type of response that we expect from children”

   synonyms: untypical

   uncharacteristic

   distinctive and not typical

   abnormal, unnatural

   not normal; not typical or usual or regular or conforming to a norm

   unrepresentative

   not exemplifying a class

   antonyms:

   typical

   exhibiting the qualities or characteristics that identify a group or kind or category

   characteristic

   typical or distinctive

   emblematic, exemplary, typic

   being or serving as an illustration of a type

   representative

   serving to represent or typify

   regular, veritable

   often used as intensifiers

   true

   conforming to definitive criteria
2. adjective

   deviating from normal expectations; somewhat odd, strange, or abnormal
   “these days large families are atypical”

   “atypical clinical findings”

   “atypical pneumonia”

   synonyms: irregular

   abnormal, unnatural

   not normal; not typical or usual or regular or conforming to a norm