Definition from Wiktionary, the free dictionary
See also Appendix:Variations of "ab"
- Able seaman; able-bodied seaman
- aid to blind
- airman basic
- (medicine) antibody
- artium baccalaureus
- (baseball) at bat
- A blood type of the ABO system that has a both blood antigens and may receive all blood types, and donate to AB.
- “AB” in The American Heritage® Dictionary of the English Language, Fourth Edition, Houghton Mifflin Company, 2000.
- “AB” in Dictionary.com Unabridged, v1.0.1, Lexico Publishing Group, 2006.
Alternative forms 
- Ab (Finland Swedish, only sense "aktiebolag" below)
- A blood type.
- (politics) Initialism of Avrupa Birliği (European Union).