Vowel, obviously, but try to come up with a word that is permissible according to the rules of the game in Scrabble and consist only of vowels. All my friends after a short thought called the same thing - “AI”, and explained that it was “golden as the sky”. Meanwhile, in the dictionary of the Russian language of Ozhegov (75,000 words), after the "Aza", "stork" follows, and, therefore, this word cannot be exhibited.