noun
black rat; black mouse
Literal meaning: a rat or mouse with black fur. Used in everyday contexts.
倉庫で黒鼠を見つけた。
I found a black rat in the warehouse.
noun
deceitful employee; unfaithful servant
Figurative, somewhat dated expression for a servant or employee who steals from or betrays their master/employer. Often used in historical or dramatic contexts.
That deceitful employee at the merchant house was falsifying the books.
noun
Color term referring to a dark gray shade, named after the fur color of a black rat. Less common than 濃い灰色.
この着物の地色は黒鼠に染めてある。
The base color of this kimono is dyed dark gray.
Compound of 黒 (black) and 鼠 (rat/mouse). The figurative sense likely arose from the image of a rat stealing food, extended to a dishonest servant. The color sense derives from the animal's fur.