foundations: the deep supports a thing rests on, used above all for the base of the world itself
This word never stands alone. It always turns up in the plural, in the phrase "the foundations of" something, and in almost every case the something is the world: the earth, the mountains, the heavens.
Behind it is a picture, not a theory. The world is spoken of the way a building is spoken of, as a structure that stands because something underneath holds it up. God is the one who set those supports in place, and they are the last thing anyone expects to move. That is exactly why poets and prophets reach for the word at only two moments: when the world's base is being laid or measured, and when it is being shaken. The things said to have foundations are worth noticing:
- the earth, in most of the word's appearances
- the mountains, in the Song of Moses and in Psalm 18
- the heavens, in David's song in 2 Samuel 22
Twice the word comes back down to ordinary masonry, the base course of stone under a town: the age-old footings that returning exiles will raise up again in Isaiah 58, and the foundation stones of Babylon that Jeremiah says no builder will ever quarry from that ruin. Those two uses are the plain sense the cosmic ones borrow.
It comes from the verb יָסַד, "to found" or "to lay a foundation." A second Hebrew word for a base, יְסוֹד, does the ordinary building work, naming the ledge at the foot of the altar and the footing of walls, while this word keeps mostly to the supports of the world.