Charles Ellicott Commentary Psalms 18:9

"He bowed the heavens also, and came down; And thick darkness was under his feet." — Psalms 18:9 (ASV)

(9) Darkness. —Better, black cloud. The dark masses of rain-cloud are now gathered, and bend to the earth under the majestic tread of God. (Compare to Nahum 1:3, and the clouds are the dust of his feet. Compare also to Psalms 144:5.)