It is so deep that it cannot be measured. It is a metaphor for being elusive about things.

Pronunciation: shēnbùkěcè

Origin: Ming Yuan Hongdao, "Roaring Mountain": "The stone and bone under the mountain was searched away by the smith's, and the water accumulated as a pool, and the hole was as black as ink when I looked at it, so deep that it was impossible to measure."

Interpretation in vernacular: The stones under the mountain were searched away by the craftsmen, and the water accumulated into a pool, and the hole was as black as ink, unfathomably deep.

Expanded Information

Proximate Meaning:

1. Highly Profound and Inexplicable

Pronunciation: gāoshēnmòcè

Interpretation: Highly profound in a degree that can't be guessed. Describes a person who is difficult to understand.

Origin: Song Gao Xisun ("讳略") cites "物类相感志"："Beyond the East China Sea is a wilderness; there is a mountain in the middle of the sea; it is scorched and confronted; it is unfathomable in its high and deepness."

Interpretation in vernacular: Beyond the East China Sea there is a desert; in the sea there is a mountain; it is scorched and confronted; it is unfathomable.

2. inscrutable

Pronunciation: bùkězhuōmō?

Interpretation: elusive: to speculate, to anticipate. It refers to the inability to guess and estimate people or things.

Source: Lao She, Zhao Ziyi, Volume 18: However, this sliced meat and that chewed rice seem to contain some inscrutable secrets.