What is the authority for the use of the expression "magic-practicing priests" New World Translation of the books of Genesis, Exodus and Daniel? (hhartumim')

The Hebrew word translated "magic-practicing priest" in Genesis, Exodus and Daniel, as, for instance, in Genesis 41:8, is hhartumim'. This word is defined by the Lexicon in Old Testament Books by Koehler and Baumgartner, Volume I, page 333, column 1, as "epithet of magic practicing priests," and it shows the ancient derivation of the word. It also suggests rendering the word in translations as "soothsayer priests". This lexicon was published in completion in 1951.

This rendering of the New World Translation is therefore both literal and explicit, in keeping with its being a literal translation. - Taken from The Watchtower 1961 5/15 320

This Hebrew word ocurrs, always in the plural, at Gen.41:8, 24; Ex.7:11, 22; 8:7, 18, 19; 9:11(twice); Dan.1:20; 2:2, 10, 27; 4:7, 9; 5:11. The New Revised Standard Version(1989) and the King James version(1611) translates it as "magicians."

The NIV Hebrew-Greek Key Word Study Bible states under this word: "Hartom; from harah...engraving tool. Magician. Always occurs in the plural form. Denotes Egyptian and Babylonian sages who practiced sorcery."- Old Testament Lexical Aids, p. 1517, AMG Publishers, 1996.

The New International Dictionary of Old Testament Theology and Exegesis: "soothsayer priest, possibly an Egyp[tian] loan word." Volume 2, page 273, Paternoster Press, UK, 1997.

Strongs Number: 2748

Goodrick/Kohlenberger: 3033