In the LXX hymnos appears in six titles of the Psalms:

Psalm 6:1
εἰς τὸ τέλος ἐν ὕμνοις ὑπὲρ τῆς ὀγδόης ψαλμὸς τῷ Δαυιδ

Psalm 54:1
εἰς τὸ τέλος ἐν ὕμνοις συνέσεως τῷ Δαυιδ

Psalm 55:1
εἰς τὸ τέλος ἐν ὕμνοις συνέσεως τῷ Δαυιδ

Psalm 66:1
εἰς τὸ τέλος ἐν ὕμνοις τῷ Δαυιδ

Psalm 67:1
εἰς τὸ τέλος ἐν ὕμνοις ψαλμὸς ᾠδῆς ὁ θεὸς

Psalm 75:1
εἰς τὸ τέλος ἐν ὕμνοις ψαλμὸς τῷ Ασαφ ᾠδὴ πρὸς τὸν Ἀσσύριον

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Hymnos is used in the LXX in Nehemiah 12:46 to describe the songs of David and Asaph. (ᾀδόντων καὶ ὕμνον καὶ αἴνεσιν τῷ θεῷ)