Easton's Bible Dictionary (1897)
Instructing, occurs in the title of thirteen Psalms (32, 42, 44, etc.). It denotes a song enforcing some lesson of wisdom or piety, a didactic song.
Smith's Bible Dictionary (1863)
(song of wisdom), the title of thirteen Psalms 32,45,44,45,52-55,74,78,68,69,142 Ewald regards (Psalms 47:7) (Authorized Version, “sing ye praises with understanding; ” Heb. maschil) as the key to the meaning of maschil, which in his opinion is a musical term denoting a melody requiring great skill in its execution.
Hastings' Dictionary of the Bible (1898)
MAS'CHIL is found in the title or inscription of thirteen Psalms — namely, 32, 42, 44, 45, 52-55, 74, 78, 88, 89, 142 — and is by some explained as an aesthetical term meaning "didactic," by others as a musical term referring to the melody.