From BiblePortal Wikipedia

Holman Bible Dictionary [1]

 Psalm 88:1

Easton's Bible Dictionary [2]

 Psalm 88

Morrish Bible Dictionary [3]

See Mahalath

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [4]

(Heb. le-annoth', לְעִנּוֹת ,for Answering, i.e. singing; Sept. Τοῦ Ἀποκριθῆναι , Vulg. Ad Respondendurn ) , a musical direction occurring in the title of Psalms 88, and denoting that it was to be chanted in the manner indicated by the associated terms. (See Book Of Psalms).