Comprehensive resource for understanding and mastering English idioms
The idiom "black mood" refers to a state of sadness, depression or melancholy. It is often used to describe someone who is feeling down, upset, or out of sorts. The term "black" is not meant to be taken literally, but rather as a metaphor for the depth and intensity of the person's emotions.
The origin of the idiom "black mood" is not entirely clear, but it has been in use since at least the 17th century. It may be related to the idea that people who are feeling down or depressed tend to have a darker outlook on life, or to the fact that some cultures associate darkness with sadness and melancholy. Over time, the idiom has become more commonly used in everyday language as a way to describe someone who is feeling blue.