I've just noticed that if you look in several English and Mongolian dictionaries that the Cyrillic Mongolian word "khan" is given as either "хан" with a short vowel, or "хаан" with a long vowel.
(So far the only traditional Mongolian script I can find is "ᠬᠠᠭᠠᠨ", but I'm not sure which OSes / web browsers will render that correctly on Stack Exchange.)
Vowel length is usually significant in Mongolian as in other "Altaic" languages. Is this an exception? Or was there some spelling reform in Mongolian that changed it over the years? Or are some sources simply wrong? Maybe they are both Mongolian words with slightly different senses?
- English Wiktionary "khan" etymology section
- English Wiktionary "хан"
- Mongolian Wiktionary "хан"
- Global Pocket Dictionary "хан" (defined as "khan")
- Global Pocket Dictionary "хаан" (defined as "king", "emperor", "monarch")