The deep; the sea; the ocean.

An abyss.

To cause to sink deeply; to cause to dive or penetrate far down.

To dive deeply; to penetrate.

Descending far below the surface; opening or reaching to great depth; deep.

Very deep; very serious

Intellectually deep; entering far into subjects; reaching to the bottom of a matter, or of a branch of learning; thorough

“a profound investigation”