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Smith's Bible Dictionary [1]

Michtam. (Golden Psalm). This word occurs in the titles of six psalms,  Psalms 16:1;  Psalms 56:1;  Psalms 57:1;  Psalms 58:1;  Psalms 59:1;  Psalms 60:1, all of which are ascribed to David.

The marginal reading of our Authorized Version is "a golden psalm," while, in the Geneva version, it is described as "a certain tune." From the position which it occupies in the title, we may infer that michtam is a term applied to these psalms, to denote their musical character, but beyond this everything is obscure.

Fausset's Bible Dictionary [2]

In the titles of some of David's psalms: Psalm 16; Psalm 56-60. Not "golden" as margin, but a "secret," conducting us into the depths of the divine life, "the secret of Jehovah" which is "with them that fear Him" ( Psalms 25:14); from Hebrew " Katham " to conceal, Arabic Katama . David delighted in enigmatical titles. Less pointedly Gesenius explains it "writing," Miktab ( Isaiah 38:9).

Morrish Bible Dictionary [3]

This word occurs in the headings of  Psalm 16;  56 - 60. Its meaning is uncertain. The margin of the A.V. reads 'a golden psalm.' Gesenius and others suppose the word michtam to be equivalent to miktab, which in  Isaiah 38:9 is translated 'writing,' hence a 'poem, psalm, song.' The LXX translates it 'a writing of David.'

American Tract Society Bible Dictionary [4]

Prefixed to  Psalm 16:11 , and meaning golden, profound, or as some think, a writing or song, as in  Isaiah 38:9 .

Holman Bible Dictionary [5]

 Psalm 16:1 Psalm 56-60 Isaiah 38:9 miktab

Easton's Bible Dictionary [6]

 Psalm 16 5660-60 Kethem

Hastings' Dictionary of the Bible [7]

Michtam See Psalms, p. 772 a .

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [8]

(Heb. miktam', מַכְתָּם , prob. for מַכְתָּב Written; Sept. Στηλογραφία , Vulg. tituli inscriptio), a term found in the titles of several psalms (16, 56, 57, 58, 60), and signifying a writing, i.e., a poem or song (see Gesenius, Thesaur. p. 724), like מַכְתָּב (Miktab', "writing," in  Isaiah 38:9). Others (as Luther, after Aben-Ezra, Kimchi, and others) unaptly translate it golden, i.e., precious, distinguished, as if from כֶּתֶם gold. Still others (as Hezel, Ewald) refer to an Arabic root meaning to Conceal, as if written from retirement, or in a plaintive strain; and some (after the rabbins) make it a compound of מָךְ וְתָם , i.q. Humble And Perfect, referring to David. (See Psalms).