What is "deep of night"

Deep \Deep\, n.

1. That which is deep, especially deep water, as the sea or ocean; an abyss; a great depth.

   Courage from the deeps of knowledge springs.
   --Cowley.

   The hollow deep of hell resounded.
   --Milton.

   Blue Neptune storms, the bellowing deeps resound.
   --Pope.

2. That which is profound, not easily fathomed, or incomprehensible; a moral or spiritual depth or abyss.

   Thy judgments are a great deep.
   --Ps. xxxvi. 6.

   Deep of night, the most quiet or profound part of night; dead of night.

   The deep of night is crept upon our talk.
   --Shak.