IPA: /ˌætrəˈbɪliəsnəs/
KK: /ˌætrəˈbɪliəsnəs/
The state of being sad or gloomy, often with a feeling of deep sadness or depression.
His atrabiliousness made it difficult for him to enjoy the party.
Atrabiliousness is formed from "atra-" (from Latin "ater", meaning black or dark) and "bilis" (from Latin "bilis", meaning bile). The suffix "-ness" indicates a state or quality. The word describes a state of being melancholic or gloomy, originally associated with the black bile in ancient medical theory, which was thought to cause such dispositions.
Think of 'darkness' ('atra-') and 'bile' ('bilis') to remember that 'atrabiliousness' refers to a state of being gloomy or melancholic.