Qinghai Lake
Names

Qinghai is the atonal pinyin romanisation of the Mandarin pronunciation of the Chinese name 青海. Although modern Chinese distinguishes between the colors blue and green, this distinction did not exist in classical Chinese. The color 青 (qīng) was a "single" color inclusive of both blue and green as separate shades. The name is thus variously translated as "Blue Sea", "Green Sea", "Blue-Green Sea", "Blue/Green Sea", etc. For a time after its wars with the Xiongnu, Han China connected the lake with the legendary "Western Sea" assumed to balance the East China Sea, but as the Han Empire expanded further west into the Tarim Basin other lakes assumed the title. The former names Chinghai, Ch'ing-hai, or Ch'inghai Lake are based on the Wade–Giles romanisation of the same Chinese name.

Qinghai Lake is also known as Koko Nor from its Classical Mongolian name ᠬᠥᠬᠡ ᠨᠠᠭᠤᠷ. The modern Mongolian form of the same name is Höhnuur (Хөхнуур). Similar to Chinese, Classical Mongolian used ᠬᠥᠬᠡ inclusive of both the color of the sky and fresh grass, but now uses xöx specifically for deep or dark blue distinguished both from light blue (цэнхэр, tsenher) and green (ногоон, nogoon). Classical Mongolian also did not distinguish between lakes and larger bodies of water. The Chinese name, using "sea" rather than "lake," is thus an overly literal calque of this name, used by the Upper Mongols, some of whom made up the local ruling class during the standardization of western Chinese toponyms in the Qing dynasty. Similar use of the Chinese word for "sea" to translate Mongolian lake toponyms can be seen elsewhere around Qinghai, as with Lake Heihai ("Black Sea") in the Kunlun Mountains.

The Tibetans also separately calqued the name as Mtsho-sngon-po or Tso ngönpo (མཚོ ་ སྔོན་པོ ་, "Blue Lake or Sea").
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