A form of the word Chingiz (spelt in many popular roman orthographies as Chinggis) is first attested in a Turkic stele commemorating the governor Alp Urungu of the Tuva region probably during the reign a later Uighur or Kirghiz Khan. It doesn’t seem like the Chingiz in it is native to Turkic as it is not found in most Turkic branches & no where else in early Turkic (e.g. the Blue Turk steles). It is likely a Mongolic loan suggesting contact with pre-Chingizid Mongolic peoples & the nobility in the Uighur or the Kirghiz Khanates.
It’s meaning in the Turkic stele is unclear. It is used as an adjective to describe the people/clansmen of the Alp Urungu in his obituary. The Turkicists take it to mean tough or fierce. That seems hard to justify. Whether it meant oceanic or expansive? Plausible but unclear.