black (color) / a black (person) / Ellipsis of ブラックコーヒー (burakku kōhī, “black coffee”). / Ellipsis of ブラック企業 (burakku kigyō, literally “black company”).

brutal, in the style of a ブラック企業 (burakku kigyō, literally “black company”)

(astronomy) a black hole

black coffee (coffee served without cream or milk)

a black bass

"black company"; an exploitative firm that abuses employees or offers poor working conditions

ridiculous (oppressive, etc.) school regulation

black light

dangerous body of water / (figuratively) (of politics or economic) unsuitable status

stairs used in emergencies