Old English, of Germanic origin; from an Indo-European root shared by Latin in- and Greek a-.
The prefixes un- and non- both mean ‘lacking’ or ‘not,’ but there is a distinction in terms of perspective. The prefix un- tends to be stronger and less neutral than non-. Consider, for example, the differences between unacademic and nonacademic, as in his language was refreshingly unacademic; a nonacademic life suits him.
Definition of un- in:
- The British & World English dictionary