AD

1. Absolute Design
2. Accidental discharge
3. Action Directe (terrorist group)
4. Active Directory
5. Active Directory
6. Active Disassembly
7. Active duty
8. Addison's disease
9. Administrative domain
10. Aggregate demand
11. Air defense
12. Air Department
13. Airworthiness Directive
14. Akcionersko društvo 
15. Aktsionerno drujestvo
16. Algemeen Dagblad
17. Alzheimer's disease
18. American Dad!
19. Anaerobic digestion
20. Analog Devices
21. Analog-to-digital converter
22. Animation Domination
23. Anno Domini
24. Anti-diarrheal
25. Antiproton Decelerator
26. Approximate digestibility
27. Architectural Digest
28. Arrested Development (TV series)
29. Art director
30. Assistant director
31. asymmetric dihydroxylation
32. Athletic director
33. Atopic dermatitis
34. Atypical depression
35. audio description
36. Audio description
37. Autodynamics
38. Automatic differentiation
39. Autosomal dominant
40. Axiom of determinacy