The game accepts about 53,000 English words of 3–9 letters, taken from the 12dicts word list (2of12inf): words that appear in at least two of twelve everyday dictionaries. All plurals and verb forms count. No proper names, no abbreviations — think crossword dictionary rather than Scrabble arsenal.
A smaller list of about 13,000 common words is used behind the scenes: it guarantees the opening board offers familiar words, and powers the thin air warning when common words are running out.