Bad mood: one brought down with others? (6)
I believe the answer is:
domino
'bad' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for domino that I've seen before include "Small black block with 0 to 6 white dots" , "Black and white game piece" , "Black tile with white dots" , "one coming down with many others?" , "Rectangular block used in game" .)