The most important name for God in the OT is the tetragrammaton YHWH (occurs about 6,800 times), usually pronounced ‘Yahweh,’ though the known pronunciation was lost in the postexilic period. Due to the increasing sanctity attached to the name and the consequent desire to avoid misuse, the title Adonai (Heb., ‘My Great Lord’) was pronounced in place of the tetragrammaton. In written texts the vowels of Adonai were combined with the consonants YHWH to remind readers to pronounce Adonai instead of Yahweh. The incorrect hybrid, ‘Jehovah,’ arose from Christian misunderstanding in the late Middle Ages. The respect for the sanctity of the personal name of God is reflected in modern Judaism.
Achtemeier, P. J., Harper & Row, P., & Society of Biblical Literature. (1985). Harper's Bible dictionary (1st ed.) (p 685). San Francisco.