black arts
n. C / Un. practices involving magic or dark powers that people use to try to control events or see the future. You usually see this phrase when people talk about secrets, mystery, or stories about witches and wizards.
n. practices associated with magic, sorcery, or the use of supernatural powers for malevolent or selfish ends. Often used metaphorically in modern contexts to describe complex, obscure, or secretive techniques in fields like technology or politics.
The old stories tell of a wizard who practiced the black arts.
To many outsiders, the high-frequency trading strategies used by the firm seemed like a form of financial black arts.
Throughout history, practitioners of the black arts were often marginalized figures whose supposed mastery over the occult was viewed as both a threat to the social order and a source of forbidden knowledge.
Usually takes the plural form 'black arts' when referring to the general field, though 'black art' may appear when describing a specific skill as a metaphorical craft.