The ancient Greeks first used this term to describe the great administrative districts of Egypt (and their term 'nomarch' for the official who governed the district), and Egyptologists have retained these words. Probably based on the prehistoric tribal divisions, the country was divided into thirty-eight or thirty-nine districts by the Old Kingdom, and by the Late Period, these had increased to forty-two.
Biographical Dictionary of Ancient Egypt by Rosalie and Antony E. David
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Greek name for the 42 provincial divisions of Egypt known as sepat to the Egyptians. There were traditionally 22 Upper Egyptian nomes and 20 Lower Egyptian nomes, each with its own standard and symbols. The governors of the nomes, known as nomarchs in Greek, tended to increase their power at times of weakness of the central government, notably during the First Intermediate Period, but their powers were curbed during Dynasty 12, and the offices may well have been suppressed under Senusret III.
Historical Dictionary Of Ancient Egypt by Morris L. Bierbrier
Ancient Egypt. A Reference Guide. EdwART. 2011.