Gloom is darkness you can still half see through, and it presses down on you. The light in a shed at dusk, a corridor with one bulb gone, a February afternoon at four o'clock.
The word holds two things at once: dim light and low spirits. A hallway can be full of gloom and so can a family after bad news, and English does not bother to keep the two apart. Gloomy is the adjective and does most of the daily work — a gloomy corridor, a gloomy forecast, a gloomy man who expects the worst. The fixed pair is doom and gloom, the talk of people waiting for disaster. Gloom is uncountable: you sit in the gloom, never in a gloom.
1noungloomPartial darkness in which you can barely make things out.
“He felt along the wall for the switch in the gloom.”
synonyms: murk, dimness
2nounfeelingA feeling of sadness and hopelessness.
“Gloom settled over the office when the news came through.”
Too few real examples of this word to estimate which sense is commonest.
gloom is a kind of darkness.
The surprise in gloom is its family. Old English glōm meant twilight, and it comes from Proto-Germanic *glōmaz, 'gleam, shimmer, sheen', on a Proto-Indo-European root *ǵʰley- meaning to gleam or glow. So gloom is a cousin of gleam, glow and the gloaming: the dark word grew out of words for light.
Proto-Indo-European
*ǵʰley- — to gleam, shimmer, glow
Proto-Germanic
*glōmaz — gleam, shimmer, sheen
Proto-West Germanic
*glōm
Old English
glōm — gloaming, twilight, darkness
Middle English
*gloom
English, today
gloom
From Middle English gloom, glom, from Old English glōm (“gloaming, twilight, darkness”), from Proto-West Germanic glōm, from Proto-Germanic glōmaz (“gleam, shimmer, sheen”), from Proto-Indo-European ǵʰley- (“to gleam, shimmer, glow”). The English word is cognate with Norwegian glom (“transparent membrane”), Scots gloam (“twilight; faint light; dull gleam”).
Etymology from Wiktionary, CC BY-SA