A fictional word, most likely a misspelling of "vocabulary".
It is called the word horde. Lexicon, vocabulaty, or word stock.
If you have an adequate vocabulaty, no letters are hard to use in scrabble. Here are the letters that might be more difficult than others, so they are worth more points: 5 points: K×1 8 points: J×1, X×1 10 points: Q×1, Z×1