gloom. n. 1. partial or total darkness. 2. a state of depression or melancholy. 3. an appearance or expression of despondency or melancholy.. a. Partial or total darkness; dimness: switched on a table lamp to banish the gloom of a winter afternoon. b. A partially or totally dark place, area, or location. 2. a. An atmosphere of melancholy or depression: Gloom pervaded the office. b. A state of melancholy or depression; despondency.