ab- ( BrE AmE ¦)æb, əb —As a true prefix meaning 'away', ab- is usually æb , though with unstressed and reduced-vowel variants (ab ˈ duct) . Italian is always ¦æb when it means 'cgs unit' ( ˈ abvolt, ˌ ab ˈ coulomb). With a vaguer meaning, it is mostly əb (ab ˈ stain) unless stressed ( ˈ abdicate, ˈ abstract).
AB-
Meaning of AB- in English
Longman Pronunciation English Dictionary. Английский словарь произношений Longman. 2012