Easton's Bible Dictionary (1897)
Occurring only in the title of Psalm 9. Some interpret the words as meaning “on the death of Labben,” some unknown person. , of Absalom (2 Sam. 18:33). Others again have taken the word as the name of a musical instrument, or as the name of an air to which the psalm was sung.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
R. " This interpretation harmonizes well with the contents of the Psalm. But the titles to the Psalms are often enigmas.