2 Old HSK word(s): ☊不觉 ** C ☊不知不觉 ** D
人不知鬼不觉* *

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

人 man / people / mankind / someone else
不 no, not / un- / negative prefix
知 know, perceive, comprehend
鬼 ghost / spirit of dead / devil
Hsk Characters:
HSK -Characters and beyond:
GbBig5EngRadMegaTripleMultilingual

Korean:
0 NHSK word(s):
KOREAN6000 word(s):
0 KOREAN 2500 New HSK words):
1 KOREAN Sentence(s):
她不觉得无聊。 + 그녀는 안 심심해요. keunyeoneun an shimshimhaeyo.