CK

1. Calvin Klein
2. Candidate key
3. Carbon Kevlar (composite fabric)
4. Carnal Knowledge
5. Carrie Kelley
6. Casein Kinase (enzyme)
7. Cask
8. Cement Kiln
9. Center Keep (gaming)
10. Centralni Komite
11. Certified Kinesiologist
12. Chairman King 
13. Chaka Khan
14. Chatham-Kent (Canada)
15. Chevrolet C/K
16. Chicken Katsu
17. Chidamber and Kemerer (metrics suite)
18. China Cargo Airlines's IATA code
19. Chris Kirkpatrick (NSYNC member)
20. Chuck Klosterman (writer)
21. Circle K (Community Service Group)
22. Circuit
23. Circus King
24. Citizen Kane
25. Citizen Kane (Orson Welles movie)
26. Civilinis kodeksas
27. Ck (digraph)
28. C-K theory
29. Clark Kent
30. Clark Kent (Superman)
31. Cocos (Kneeling) Islands
32. Commander Keen
33. Common Knowledge
34. Compartment Key
35. Composite Corridor
36. Con Kolivas
37. Conductive Keratoplasty
38. Confirmed Kills
39. ConsoleKit
40. Containerized Kitchen
41. Conversion Kit
42. Cook Islands (country code, top level domain)
43. Cop Killer
44. Core Knowledge
45. Corner kick
46. Corner Kick (soccer)
47. Cranbrook Kingswood
48. Creatine Kinase (blood test)
49. Creek
50. Crip Killer (gangs)
51. Crip-Killer
52. Crusader Kings (video game)
53. Cyanogen chloride
54. Cyanogen Chloride
55. Cyto Keratin (immunohistochemistry)