figurative. (a) ‘Black’, wicked, iniquitous. (b) Baleful, malignant.

Having or demonstrating evil intent; malignant, deadly; sinister.

? Belonging to a ‘flask’ or muddy pool.

figurative. Lacking moral or spiritual goodness; evil, wicked; iniquitous.

gen. Black. Chiefly poetic and rhetorical. Of agencies personified.