TT #67 · Parashas Noach · Sixth Aliyah · Passuk 10:10
And the beginning of his kingdom was Babylon, and Erech, and Akkad, and Calneh, in the land of Shinar.
Torah Temimah points to R’ Yochanan (why called Shinar).
E-Daf image — Yoma 10a (size=3)
“In the land of Shinar” — Why was it called Shinar? R’ Yochanan said: Because all the dead of the Flood were shaken down there.
Custom (etymology of Shinar).
Shinar is so named because the corpses of the Flood generation were deposited/shaken down into its depths.