Easton's Bible Dictionary: M. G. Easton, M.A., D.D.

Deep

Used to denote

1. the grave or the abyss (Rom. 10:7; Lk. 8:31);
2. the deepest part of the sea (Ps. 69:15);
3. the chaos mentioned in Gen. 1:2;
4. the bottomless pit, hell (Rev. 9:1, 2, 11:7, 20:13).