MAHALATH (mā'ha-lăth, Heb. mahălath, sickness)
A daughter of Ishmael whom Esau took for his third wife (Gen.28.9).The first wife of Rehoboam; she was a granddaughter of David (2Chr.11.18).A musical term in the heading of Ps.53.1-Ps.53.6 and Ps.88.1-Ps.88.18.
International Standard Bible Encyclopedia (1915)
(1) In Ge 28:9 the name of a wife of Esau, daughter of Ishmael, and sister of Nebaioth, called in 36:3, BASEMATH (which see). The Samaritan Pentateuch, however, throughout Genesis 36 retains "Mahalath." On the other hand, in 26:34 Basemath is said to be "the daughter of Elon the Hittite," probably a confusion with Adah, as given in 36:2, or corruption may exist in the lists otherwise.
(2) One of the 18 wives of Rehoboam, a grand-daughter of David (2Ch 11:18).
(3) The word is found in the titles of Ps 53 (the Revised Version (British and American) "set to Mahalath") and Ps 88 (the Revised Version (British and American) "set to Mahalath Leannoth," margin "for singing"). Probably some song or tune is meant, though the word is taken by many to denote a musical instrument. Hengstenberg and others interpret it as indicating the subject of the Psalms.
Music; Musical Instruments