shēn​bù​kě​cè

enigmatic

深不可测 (深不可測) shēn​bù​kě​cè
enigmatic idiom
incomprehensible or impossible to predict; describing someone's mind, character, or motives
unfathomable expression
deep and unmeasurable in a physical sense, such as water or a chasm

Frequency

Movie subtitles
0.300 per million appears in 0% of films
Written text
1.02 per million

Sources

Definitions
CC-CEDICT