To settle down; subside; hold back.

And God remembered Noah, and every living thing, and all the cattle that was with him in the ark: and God made a wind to pass over the earth, and the waters ASSWAGED; the fountains also of the deep and the windows of heaven were stopped, and the rain from heaven was restrained; ( Genesis 8:1-2 )

Dictionary of Words from the King James Bible. Public Domain. Copy freely.