There are 101 legal 2-letter words in the OWL2 official tournament word list. All of them are listed below in "playrank order," meaning the most often played word of the bunch is listed first, the second most often played word of the bunch is listed second, and so on down the list. So QI is the most often played 2-letter word, RE is second, and MM is the least often played. QI is in fact the most often played word of any length in Scrabble by a large margin.
Regardless of the ordering below, every one of these words gets played very often and any serious Scrabble player must memorize them all.
1. qi
2. re
3. er
4. in
5. it
6. et
7. en
8. za
9. jo
10. ne
11. we
12. id
13. ti
14. de
15. ed
16. or
17. el
18. ar
19. li
20. ef
21. if
22. fe
23. go
24. ag
25. ta
26. xi
27. ex
28. ad
29. to
30. at
31. oe
32. do
33. on
34. aw
35. na
36. an
37. be
38. un
39. pe
40. no
41. ut
42. ye
43. wo
44. ow
45. ae
46. od
47. al
48. fa
49. la
50. bi
51. oi
52. pi
53. lo
54. eh
55. nu
56. of
57. he
58. ab
59. op
60. ax
61. ki
62. em
63. ai
64. hi
65. me
66. ya
67. ox
68. pa
69. es
70. mi
71. ay
72. ka
73. si
74. is
75. ba
76. ha
77. aa
78. oy
79. yo
80. up
81. ah
82. bo
83. am
84. xu
85. ma
86. oh
87. ho
88. om
89. as
90. so
91. uh
92. mo
93. os
94. um
95. by
96. mu
97. us
98. sh
99. my
100. hm
101. mm
This list is original research from ScrabbleGuru.com. Come visit us for more!