Official list of English two-letter words acceptable in the board game Scrabble
This list gives all the English two-letter words playable in Scrabble (playable everywhere except for countries that use the rival TWL dictionary; the US, Canada, Israel, and Thailand) according to the Official Scrabble Players Dictionary and Official Scrabble Words International, each of which list all permissible words from two up to about nine letters in length.
ch, although valid for Scrabble, has been questioned as to its validity as being an actual word. Ch, now considered obsolete, was very rarely found as a separate element. It is a dialectal stem fused to verbs and has the meaning "I", as in the dialectal verbs "cham" (I am) and "chave" (I have). Its inclusion in International Scrabble is due to its presence in The Chambers Dictionary, the dictionary adopted in 1980 for arbitration in official tournaments in Britain and used in the formation of the Official Scrabble Words (OSW) list.
The Dictionary Committee of the National Scrabble Association (of North America) in early 2006 added five two-letter words to the Official Scrabble Players Dictionary: fe, ki, oi, qi, and za. Oi and qi were already allowed in Official Scrabble Words International, and the remaining words have since been adopted into SOWPODS play, along with ja in SOWPODS.