Meaning of A- in English
a- combining form BrE AmE ¦eɪ, eɪ, ¦æ, æ, ə —When it has a negative meaning, this prefix is usually eɪ ( ˌ athe ˈ istic) , though in some words there are alternative pronunciations with æ or ə ( ˌ a ˈ moral, a ˈ moral) , and sometimes ə is the only form (a ˈ morphous). With other meanings, the pronunciation is regularly ə (a ˈ way, a ˈ spire), unless stressed because of a suffix, in which case it is ¦æ ( ˌ aspi ˈ ration).
Longman Pronunciation English Dictionary. Английский словарь произношений Longman. 2012