Emily Dickinson Lexicon

deep, n. [OE déop.] (webplay: great, maketh, ocean, out, sea, still, waters).

1. Unknown waters; [fig.] eternity; infinity; deity; source of hidden truths; profound depths of understanding.
2. Ocean; sea; large body of water; (see Genesis 1:2).
3. Abyss; that which is mysterious; [fig.] not easily fathomed; (see Genesis 49:25).