Meaning of AN- in English
an- ( BrE AmE ¦) æn, ən —When it is a variant of ad- , this prefix is usually ə (an ˈ nul), but æ if stressed because of a suffix ( ˈ annotate). As a negative prefix, it is usually æn ( ˌ an ˈ oxia) , undergoing reduction to ən only in a few better-known words (a ˈ nonymous).
Longman Pronunciation English Dictionary. Английский словарь произношений Longman. 2012