Official list of English two-letter words acceptable in the board game ScrabbleEdit
This list gives all the English two-letter words playable in Scrabble (playable everywhere except for countries than 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, is not an actual word; rather, it is an obsolete stem prepended to verbs and meaning "I", as in "cham" (I am) and "chave" (I have). It is included in Scrabble because the dictionary used to compile the English word lists (incorrectly) gives it as a word.
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.