Unconsciousness
Unconsciously, Involuntary
noun, な adjective
Know how 意識 is "consciousness"? What about when this consciousness doesn't exist (aka it is nothing)? That's when it becomes unconsciousness.
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. It will help to know how to read 意識, though.
彼女は無意識にその曲を口ずさんでいました。
She unconsciously hummed the tune.
その無意識にツメをかむクセは直した方がいいよ。
That involuntary habit of biting your nails should be fixed.
彼はきっと、自分と対等だと思わない人間は無意識に見下してるんだよ。
I'm sure he subconsciously looks down on anyone he doesn't consider his equal.