Which of the following words would best describe a sad or depressed atmosphere?

The term "melancholy" specifically captures the essence of a sad or depressed atmosphere. It refers to a deep, persistent sadness or sorrow that can permeate a setting or mood. In literature and everyday language, "melancholy" is often used to depict a feeling of reflective sadness, suggesting not just an emotional state but also an ambiance that evokes a sense of solemnity and introspection.

In contrast, the other terms carry different connotations. "Gregarious" describes someone who is sociable and enjoys the company of others, which contrasts sharply with a sad atmosphere. "Jocular" refers to a light-hearted, playful demeanor, hence it does not align with sadness or depression at all. "Peevish" denotes irritability or annoyance, which is related to negative feelings but does not encompass the deeper, more somber quality associated with melancholy. Therefore, "melancholy" is the most fitting choice to describe a sad or depressed atmosphere.