Fabby means: Fabby is a casual British slang intensifier meaning fabulous, great, or excellent. It's a cheerful, slightly effusive word - the kind you'd hear from an enthusiastic friend rather than in formal. It is informal slang, fine in casual speech but not suited to formal contexts. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. As a place or proper-name reference it is purely descriptive.