Ertiş is the Old Turkic name of the Irtysh River and occurs both independently and in the compound Ertiş Ügüz ‘Irtysh River’. It is repeatedly attested in the runiform inscriptions, for example in Tunyukuk 35: altun yışıg yolsızın aşdımız, ertiş ügüzüg keçigsizin keçdimiz ‘we crossed the Altai Mountains without a road and the Irtysh River without a ford’.
The etymology is disputed. Kaşgari derived the river-name from ertiş- ‘compete in passing or crossing’, an explanation rejected by Clauson as a folk etymology. A more plausible analysis derives Ertiş from ert- ‘pass, go by; flow past’ with the deverbal noun suffix -iş, giving approximately ‘passing, flowing; passage’. This remains probable rather than certain. Proposed Iranian–Yeniseian substrate etymologies are also disputed.