Why are some words in the dictionary not allowed?

Question

The word "duar" is in the dictionary, but the game rejects it - why?

Why is QI accepted, but IQ is not?

Answer 1

Words With Friends uses a public domain wordlist that is common for Internet word games called the ENABLE list.  This wordlist holds approximately 173,000 words, but you may still be able to find some words in your dictionary that are not included in the ENABLE list.  DUAR also does not appear in Scrabble's tournament wordlist, for whatever that may be worth.

QI is an alternate spelling of CHI, a kind of mystical energy.  I.Q. is generally regarded as an abbreviation for Intelligence Quotient, not a word unto itself.