Borrowed from Classical Mongolian ᠳᠣᠷᠵᠢ (dorǰi), from Classical Tibetan རྡོ་རྗེ (rdo rje, “vajra”). Compare Kalmyk Дорҗ (Dorj), Mongolian Дорж (Dorž), Buryat Доржо (Doržo).
Доржу • (Dorju)