NASPA Word List (NWL), (formerly Official Tournament and Club Word List, referred to as OTCWL, OWL, TWL), is the official word authority for tournament Scrabble in the USA, Canada and Thailand. It is based on the Official Scrabble Players Dictionary (OSPD) with modifications to make it more suitable for tournament play. Its British counterpart is Collins Scrabble Words.
North American tournament Scrabble currently uses the fourth ion of OTCWL (officially NWL2018, but variously referred to as OWL4, OTCWL2018, TWL4, and TWL2018). This version was created by the North American Scrabble Players Association (NASPA) Dictionary Committee in 2018 and took effect on March 1, 2019; it is the first version published autonomously by NASPA rather than by Merriam-Webster under their copyright.
OWL4 contains every word in the sixth ion of the Official Scrabble Players Dictionary, but also includes words considered unsuitable for that book.
The decision to bowdlerize the OSPD's third ion by removing a large number of possibly offensive words necessitated a separate, unabridged word list for tournament use. The first ion of OWL was created by the NSA Dictionary Committee, chaired by John Chew, and took effect on March 2, 1998. To avoid controversy, it was available for sale only to NSA members, and unlike the OSPD, did not include definitions. To provide additional value for tournament players, the OWL includes words whose base or inflected forms have up to nine letters, rather than the OSPD's eight. OSPD3 was created from OSPD2 by adding all appropriate words that had been added to Merriam-Webster's Collegiate Dictionary (MWCD) in the interim; OWL was then formed by restoring the possibly offensive words removed from OSPD3, and adding nine-letter words from MWCD. The 2014 update (OTCWL2014, also known as OWL3) added several thousand words from two new sources, Oxford Collegiate Dictionary Second Edition (COD2) and Canadian Oxford Dictionary Second Edition (COD2). A minor update in 2016 (OTCWL2016, also known as OWL3.1) added over a thousand nine-letter words.
Unlike the Official Scrabble Players Dictionary, OWL is a list and does not include definitions. OWL also contains words not included in OSPD because they are considered offensive, and a number of other additional words (mostly registered trademarks). Print versions of OWL can be procured from the NASPA website by NASPA members only.