1.  Partial or total darkness; thick shade; obscurity; as, the gloom of a forest, or of midnight. [1913 Webster]

2.  A shady, gloomy, or dark place or grove. [1913 Webster]
"Before a gloom of stubborn-shafted oaks." [1913 Webster]

3.  Cloudiness or heaviness of mind; melancholy; aspect of sorrow; low spirits; dullness. [1913 Webster]
"A sullen gloom and furious disorder prevailed by fits." [1913 Webster]

4.  In gunpowder manufacture, the drying oven. [1913 Webster]

1.  To shine or appear obscurely or imperfectly; to glimmer. [1913 Webster]

2.  To become dark or dim; to be or appear dismal, gloomy, or sad; to come to the evening twilight. [1913 Webster]
"The black gibbet glooms beside the way." [1913 Webster]
"[This weary day] . . . at last I see it gloom." [1913 Webster]

1.  To render gloomy or dark; to obscure; to darken. [1913 Webster]
"A bow window . . . gloomed with limes." [1913 Webster]
"A black yew gloomed the stagnant air." [1913 Webster]

2.  To fill with gloom; to make sad, dismal, or sullen. [1913 Webster]
"Such a mood as that which lately gloomed
Your fancy." [1913 Webster]
"What sorrows gloomed that parting day." [1913 Webster]

gloom, n. & v.
--n.
1 darkness; obscurity.
2 melancholy; despondency.
3 poet. a dark place.
--v.
1 intr. be gloomy or melancholy; frown.
2 intr. (of the sky etc.) be dull or threatening; lour.
3 intr. appear darkly or obscurely.
4 tr. cover with gloom; make dark or dismal.

Etymology:
ME gloum(b)e, of unkn. orig.: cf. GLUM

N  dejection, dejectedness, depression, prosternation, lowness of spirits, depression of spirits, weight on the spirits, oppression on the spirits, damp on the spirits, low spirits, bad spirits, drooping spirits, depressed spirits, heart sinking, heaviness of heart, failure of heart, heaviness, infestivity, gloom, weariness, taedium vitae, disgust of life, mal du pays, anhedonia, melancholy, sadness, il penseroso, melancholia, dismals, blues, lachrymals, mumps, dumps, blue devils, doldrums, vapors, megrims, spleen, horrors, hypochondriasis, pessimism, la maladie sans maladie, despondency, slough of Despond, disconsolateness, hope deferred, blank despondency, voiceless woe, prostration of soul, broken heart, despair, cave of despair, cave of Trophonius demureness, gravity, solemnity, long face, grave face, hypochondriac, seek sorrow, self-tormentor, heautontimorumenos, malade imaginaire, medecin tant pis, croaker, pessimist, mope, mopus, affliction, sorry sight, memento mori, damper, wet blanket, Job's comforter, cheerless, joyless, spiritless, uncheerful, uncheery, unlively, unhappy, melancholy, dismal, somber, dark, gloomy, triste, clouded, murky, lowering, frowning, lugubrious, funereal, mournful, lamentable, dreadful, dreary, flat, dull, dull as a beetle, dull as ditchwater, depressing, melancholy as a gib cat, oppressed with melancholy, a prey to melancholy, downcast, downhearted, down in the mouth, down in one's luck, heavy-hearted, in the dumps, down in the dumps, in the suds, in the sulks, in the doldrums, in doleful dumps, in bad humor, sullen, mumpish, dumpish, mopish, moping, moody, glum, sulky, out of sorts, out of humor, out of heart, out of spirits, ill at ease, low spirited, in low spirits, a cup too low, weary, discouraged, disheartened, desponding, chapfallen, chopfallen, jaw fallen, crest fallen, sad, pensive, penseroso, tristful, dolesome, doleful, woebegone, lacrymose, lachrymose, in tears, melancholic, hypped, hypochondriacal, bilious, jaundiced, atrabilious, saturnine, splenetic, lackadaisical, serious, sedate, staid, stayed, grave as a judge, grave as an undertaker, grave as a mustard pot, sober, sober as a judge, solemn, demure, grim, grim-faced, grim-visaged, rueful, wan, long-faced, disconsolate, unconsolable, inconsolable, forlorn, comfortless, desolate, desole, sick at heart, soul sick, heart sick, au desespoir, in despair, lost, overcome, broken down, borne down, bowed down, heartstricken, cut up, dashed, sunk, unnerved, unmanned, down fallen, downtrodden, broken-hearted, careworn, with a long face, with tears in one's eyes, sadly, the countenance falling, the heart failing, the heart sinking within one, a plague of sighing and grief, thick-ey'd musing and curs'd melancholy, the sickening pang of hope deferred.

N  darkness, absence of light, blackness, obscurity, gloom, murk, dusk, Cimmerian darkness, Stygian darkness, Egyptian darkness, night, midnight, dead of night, witching hour of night, witching time of night, blind man's holiday, darkness visible, darkness that can be felt, palpable obscure, Erebus, the jaws of darkness, sablevested night, shade, shadow, umbra, penumbra, sciagraphy, obscuration, occultation, adumbration, obumbration, obtenebration, offuscation, caligation, extinction, eclipse, total eclipse, gathering of the clouds, shading, distribution of shade, chiaroscuro, noctivagation, black body, hohlraum, black hole, dark star, dark matter, cold dark matter, dark, darksome, darkling, obscure, tenebrious, sombrous, pitch dark, pitchy, pitch black, caliginous, black, sunless, lightless &c (sun) (light), somber, dusky, unilluminated &c (illuminate), nocturnal, dingy, lurid, gloomy, murky, murksome, shady, umbrageous, overcast, cloudy, darkened, dark as pitch, dark as a pit, dark as Erebus, benighted, noctivagant, noctivagous, in the dark, in the shade, brief as the lightning in the collied night, eldest Night and Chaos, ancestors of Nature, the blackness of the noonday night, the prayer of Ajax was for light.