Unknown
Unclear, Uncertain, Unsure
noun, な adjective
When it's not bright, you can't see what's around you. In the dark, everything feels unknown, unclear, and uncertain.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
このホテルは、オーナーが不明です。
The owner of this hotel is unknown.
生まれた日は不明です。
The day of birth is unknown.
私の兄は今どこにいるか不明なんです。
It's uncertain where my brother is now.