Abjure means to swear off, and it applies to something you once believed. You can abjure a religious faith, you can abjure your love of another person, and you can abjure the practice of using excessive force in interrogation.
Abjure is a more dramatic way to declare your rejection of something you once felt or believed. When you see its Latin roots, it makes sense: from ab- (meaning "away") and jurare ("to swear"). When you abjure something, you swear it away and dissociate yourself with it. You might abjure the field of astrology after receiving a bad fortune, or you might abjure marriage after a bitter divorce.