From ᠨᡳᠩᡤᡠᠨ (ninggun, “six”) + ᠠᠴᠠᠨ (acan, “conjunction”). Calque of Chinese 六合.
ᠨᡳᠩᡤᡠᠨᠠᠴᠠᠨ • (ninggun acan)