Chaldeans or Chaldees
It appears that the Chaldeans (Kaldai or Kaldi) were in the earliest times merely one out of many Cushite tribes inhabiting the great alluvial plain known afterwards as Chaldea or Babylonia. Their special seat was probably that southern portion of the country which is found to have so late retained the name of Chaldea. In process of time, as the Kaldi grew in power, their name gradually prevailed over those of the other tribes inhabiting the country, and by the era of the Jewish captivity it had begun to be used generally for all the inhabitants of Babylonia. It appears that while, both in Assyria and in later Babylonia, the Shemitic type of speech prevailed for civil purposes, the ancient Cushite dialect was retained as a learned language for scientific and religious literature. This is no doubt the “learning” and the “tongue” to which reference it made in the book of Daniel (Daniel 1:4). The Chaldeans were really the learned class; they were priests, magicians, or astronomers, and in the last of the three capacities they probably effected discoveries of great importance. In later times they seem to have degenerated into mere fortune-tellers.
Smith's Bible Names Dictionary (1866).