1.  heaviness(n = noun.attribute) weightiness - the property of being comparatively great in weight; "the heaviness of lead"
is a kind of weight
has particulars: heft, heftiness, massiveness, ponderosity, ponderousness, preponderance
Antonym: lightness
Derived forms adjective heavy₅, adjective heavy₂₂, adjective heavy₁, adjective heavy₉

2.  heaviness(n = noun.feeling) Array - persisting sadness; "nothing lifted the heaviness of her heart after her loss"
is a kind of sadness, unhappiness
Derived form adjective heavy₄

3.  heaviness(n = noun.attribute) ponderousness - an oppressive quality that is laborious and solemn and lacks grace or fluency; "a book so serious that it sometimes subsided into ponderousness"; "his lectures tend to heaviness and repetition"
is a kind of uninterestingness
Derived form adjective heavy₂₅

4.  heaviness(n = noun.attribute) thickness - used of a line or mark; Array
is a kind of broadness, wideness
Derived form adjective heavy₁₂

5.  heaviness(n = noun.attribute) burdensomeness, onerousness, oppressiveness - unwelcome burdensome difficulty; Array
is a kind of difficultness, difficulty
Derived forms adjective heavy₂₄, adjective heavy₂

   The state or quality of being heavy in its various senses; weight; sadness; sluggishness; oppression; thickness. [1913 Webster]

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  dullness, heaviness, flatness, infestivity &c, stupidity want of originality, dearth of ideas, prose, matter of fact, heavy book, conte a dormir debout, platitude, dull, dull as ditch water, unentertaining, uninteresting, flat, dry as dust, unfunny, unlively, logy, unimaginative, insulse, dry as dust, prosy, prosing, prosaic, matter of fact, commonplace, pedestrian, pointless, weary stale flat and unprofitable, stupid, slow, flat, insipid, vapid, humdrum, monotonous, melancholic, stolid plodding, boring, tiresome, tedious, davus sum non Aedipus, deadly dull and boring, DDB.

N  gravity, gravitation, weight, heaviness, specific gravity, pondorosity, pressure, load, burden, burthen, ballast, counterpoise, lump of, mass of, weight of, lead, millstone, mountain, Ossa on Pelion, weighing, ponderation, trutination, weights, avoirdupois weight, troy weight, apothecaries' weight, grain, scruple, drachma, ounce, pound, lb, arroba, load, stone, hundredweight, cwt, ton, long ton, metric ton, quintal, carat, pennyweight, tod, gram, centigram, milligram, microgram, kilogram, nanogram, picogram, femtogram, attogram, balance, scale, scales, steelyard, beam, weighbridge, spring balance, piezoelectric balance, analytical balance, two-pan balance, one-pan balance, postal scale, baby scale, statics, weighty, weighing, heavy as lead, ponderous, ponderable, lumpish, lumpy, cumbersome, burdensome, cumbrous, unwieldy, massive, incumbent, superincumbent.