Official Tournament and Club Word List
The second edition of the Official Tournament and Club Word List (OTCWL2, also known as OWL2 or TWL2) is the official word list for NASPA-sanctioned club and tournament play, and contains words of up to nine letters and their inflections. (Longer words are listed in Long List.) The OTCWL2 is edited by the Dictionary Committee (whose wiki page goes into the lexicon’s history in greater detail), published by Merriam-Webster and available only from Word Gear.
The tournament word list is not available to the public in electronic form; it can be purchased in print from NSA Word Gear. The electronic word list is available to authorized SCRABBLE developers. If you are not sure if you have the correct version of the digital file, here are some statistics you can check. There are currently 101 2-letter words, 1015 3, 4030 4, 8938 5, 15788 6, 24029 7, 29766 8, 29150 9, 22326 10, 16165 11, 11417 12, 7750 13, 5059 14 and 3157 15, for a total of 178,691 words. (13 of those words are not playable using the standard 100 tiles: CLASSLESSNESSES, KNICKKNACK(S), PIZZAZZ(ES), PIZZAZZY, POSSESSEDNESSES, RAZZAMATAZZ(ES), RAZZMATAZZ(ES), SENSELESSNESSES, STRESSLESSNESS.) The master file lists all words in lower case in alphabetical order, one per line, with each line terminated by a Unix line break. It is 1763167 bytes long and has BSD checksum ('cksum -o 1') 12722, System V checkum ('cksum -o 2') 24638, 32-bit CRC ('cksum -o 3') 2022312244, ISO/IEC 8802-3:1989 checksum ('cksum') 427611949 and MD5 checksum dfd408f47cc1a324eb0ab5577910e4e3.
If your favorite word is not in the lexicon, or you think some of the words in the list shouldn't be there, you should read about how lexicons are compiled.
Incorrectly omitted from OTCWL2: CRABAPPLE (p. 98), CRABAPPLES (p. 98), DEVELOPPES (p. 118), GODDAMNDEST (p. 186), MUNCHABLES (p. 279) and VIREONINES (p.485).
Incorrectly included in OTCWL2: CRABABBLE (p. 98), CRABABBLES (p. 98), GODAMNDEST (p. 186) and WEAPONEERED (p. 491).
The word ANTEFIXAE was incorrectly omitted from the printed edition of OTCWL1.