Pronem asked about the difference between atypical and untypical.
Thank you for this question.
Because the prefixes a- and un- can both mean not, atypical and untypical have the same meaning: not typical, not usual or normal. However, the contexts in which these two words are used are different. There is also a 3rd choice with the same meaning, which will be discussed below.
1. atypical
Atypical is the most common of these choices. However, it is used mostly in formal language about medical topics, as in these examples:
These cases were atypical because the patients were diabetic.
The biopsy showed a few atypical cells.
2. untypical
Untypical is used much less often than atypical, and it is becoming rarer. When untypical is used, it is most often after the word not, as in this example:
The summer weather arrived suddenly, which is not untypical for New Orleans. (not + untypical = typical)
3. not typical
The phrase not typical is used more than untypical. Not typical can be used in a variety of contexts to talk about all kinds of topics, as shown in these examples:
