0 Old HSK word(s):
不得而知* *

Definitions from Unihan Copyright © 1991-2015 Unicode® Inc. All rights reserved.

不 no, not / un- / negative prefix
得 obtain, get, gain, acquire
而 and / and then / and yet / but
知 know, perceive, comprehend
Hsk Characters:
HSK -Characters and beyond:
GbBig5EngRadMegaTripleMultilingual