Some words are not allowed according to the rules. For example words have to be between 4 and 8 letters long.
Is your word a proper noun? If your word is a name, or frequently capitalized, it may not be accepted. Words that can be names but are also frequently not used as names are typically accepted. For example, JACK or NICK are accepted. However, capitalized names like JUPITER, TUESDAY, and FINLAND are not.
Why aren't proper nouns accepted? The game is balanced to provide the right level of challenge and fun. Proper nouns can be pretty obscure, from many different languages, and with large variations in spelling. We don't want to exclude names arbitrarily, so it makes for a better game not to go down that path.
I still think you should include my word! Great, please send feedback with whichever word(s) you think should be accepted and we'll consider adding them!