Aaaand here it is! Hox sums it up best, so let me quote him:
With the 4th volume, Temuchin becomes Chinggis Khan at last! Two things I want to note about this volume. One is the meaning of the title, "chinggis." Although this manga says it means, "supreme and strong," the matter is more complicated than that as scholars continue to debate it. To quote a section from Ratchnevsky's Genghis Khan: His Life and Legacy:
The word has been variously interpreted as 'firm', 'strong', 'righteous', 'loyal', 'hard' or 'cruel', depending upon the meaning attributed to the word ching by different Mongol tribes. In general such attributions seek to stress the quality of a 'firm and strong khan' rather than exhibiting any desire to vie with the title of Gurkhan ('Universal Ruler') which had been bestowed on Jamuka.
An alternative and probably sounder derivation, advanced quite independently by von Ramstedt and Pelliot, is from the Turkic tängiz, 'sea or ocean.' This interpretation is supported by the Mongolian equivalent dalai-yin khan on the seal of the Great Khan and the Turkic formal preamble tailai-nung han in Guyuk Kha'ans letter to Pope Innocent IV. In dalai lama, the Mongolian rendering of the Tibetan lamaistic title, rGyamts'o blama, meaning 'Ruler of the Seas' or 'Ruler of the World', dalai is used as a concept for 'universal' or 'all-embracing'; this is clearly exhibited by the juxtaposition of dalai and yeke ('great') in the Juyongguan Inscription. The title 'Oceanic Ruler' is very old. In Uighur legend Tengiz (Dengiz-khan) is the name of the youngest son of the Uighur Oguz-khan - and, despite Pelliot's phonetic objections, it may even be identified in the name of one of the sons of Attila the Hun.
Although in Rashid ad-Din's day the Mongols had forgotten the original tradition and the title was simply equated with the Mongolian word ching ('firm' or 'strong'), Rashid uses the wider interpretation of the title when he compares it with the Persian shah-an-shah. Nasir ad-Din also gives Hulegu the title padsha-i jahan ('Universal Ruler'), a non-Islamic title which, as Minorsky comments, must be a rendering of dalai-khan. The Genghiside imperial family retained this tradition into the seventeeth century, when a son of Dayan-khan bore the title erdeni dalai khan.There are, of course, more fringe theories on its meaning, such as that it's derived from the Chinese tianzi (Son of Heaven), or a rendering of the Chinese imperial first-person pronoun zhèn (朕). There are also tales in later Mongolian chronicles that it's an onomatopoeic representation of a bird cry, but these are more folklore than actual history.
The second thing I want to mention is that while the Naimans were a Turkic group, distinct from the Mongols in central Mongolia and Tungusic peoples in Eastern Mongolia and Manchuria, they were still primarily pastoral nomads and it's highly unlikely that their style of combat differed all that much from all of the horse-riding warriors across the Eurasian steppe. Or to put it simply, they did NOT use war chariots. I don't know where Yokoyama got that idea, or maybe he wanted to add them because they looked cool, but to think that the very people whose entire society changed once horses were domesticated to a point as to accommodate human riders, would build an extremely expensive yet less effective tool of war that had been abandoned by even the sedentary civilizations for almost a thousand years prior to the 13th century is just absurd.