1. dead letter(n = noun.state) non-issue - the state of something that has outlived its relevance;
is a kind of state
2. dead letter(n = noun.communication) dead mail - mail that can neither be delivered nor returned;
is a kind of letter, missive
N inutility, uselessness, inefficacy, futility, ineptitude, inaptitude, unsubservience, inadequacy, inefficiency, unskillfulness, disservice, unfruitfulness (unproductiveness), labor in vain, labor lost, labor of Sisyphus, lost trouble, lost labor, work of Penelope, sleeveless errand, wild goose chase, mere farce, tautology, supererogation, vanitas vanitatum, vanity, inanity, worthlessness, nugacity, triviality, caput mortuum, waste paper, dead letter, blunt tool, litter, rubbish, junk, lumber, odds and ends, cast-off clothes, button top, shoddy, rags, orts, trash, refuse, sweepings, scourings, offscourings, waste, rubble, debris, detritus, stubble, leavings, broken meat, dregs, weeds, tares, rubbish heap, dust hole, rudera, deads, fruges consumere natus, useless, inutile, inefficacious, futile, unavailing, bootless, inoperative, inadequate, inservient, unsubservient, inept, inefficient, of no avail, ineffectual, incompetent, stale, flat and unprofitable, superfluous, dispensable, thrown away, abortive, worthless, valueless, priceless, unsalable, not worth a straw, dear at any price, vain, empty, inane, gainless, profitless, fruitless, unserviceable, unprofitable, ill-spent, unproductive, hors de combat, effete, past work, obsolete, fit for the dust hole, good for nothing, of no earthly use, not worth having, not worth powder and shot, leading to no end, uncalled for, unnecessary, unneeded, uselessly, to little purpose, to no purpose, to little or no purpose, Int, cui bono?, what's the good!, actum ne agas, chercher une aiguille dans une botte de foin, tanto buon che val niente.
N laxity, laxness, looseness, slackness, toleration, freedom, anarchy, interregnum, relaxation, loosening, remission, dead letter, brutum fulmen, misrule, license, licentiousness, insubordination, lynch law, nihilism, reign of violence, dethronement, deposition, usurpation, abdication, lax, loose, slack, remiss, weak, relaxed, licensed, reinless, unbridled, anarchical, unauthorized, adespotic.
N impotence, inability, disability, disablement, impuissance, imbecility, incapacity, incapability, inaptitude, ineptitude, incompetence, unproductivity, indocility, invalidity, disqualification, inefficiency, wastefulness, telum imbelle, brutum fulmen, blank, blank cartridge, flash in the pan, vox et proeterea nihil, dead letter, bit of waste paper, dummy, paper tiger, Quaker gun, inefficacy, failure, helplessness, prostration, paralysis, palsy, apoplexy, syncope, sideration, deliquium, collapse, exhaustion, softening of the brain, inanition, emasculation, orchiotomy, orchotomy, cripple, old woman, muff, powder puff, creampuff, pussycat, wimp, mollycoddle, eunuch, powerless, impotent, unable, incapable, incompetent, inefficient, ineffective, inept, unfit, unfitted, unqualified, disqualified, unendowed, inapt, unapt, crippled, disabled, armless, harmless, unarmed, weaponless, defenseless, sine ictu, unfortified, indefensible, vincible, pregnable, untenable, paralytic, paralyzed, palsied, imbecile, nerveless, sinewless, marrowless, pithless, lustless, emasculate, disjointed, out of joint, out of gear, unnerved, unhinged, water-logged, on one's beam ends, rudderless, laid on one's back, done up, dead beat, exhausted, shattered, demoralized, graveled, helpless, unfriended, fatherless, without a leg to stand on, hors de combat, laid on the shelf, null and void, nugatory, inoperative, good for nothing, ineffectual, inadequate, inefficacious, der kranke Mann, desirous still but impotent to rise, the spirit is willing but the flesh is weak.
N dereliction of duty, fault, sin, non-observance, non-performance, neglect, relaxation, infraction, violation, transgression, failure, evasion, dead letter.
N meaninglessness, unmeaningness, scrabble, empty sound, dead letter, vox et praeterea nihil, a tale told by an idiot, full of sound and fury, signifying nothing, sounding brass and a tinkling cymbal, nonsense, utter nonsense, gibberish, jargon, jabber, mere words, hocus-pocus, fustian, rant, bombast, balderdash, palaver, flummery, verbiage, babble, baverdage, baragouin, platitude, niaiserie, inanity, flap-doodle, rigmarole, rodomontade, truism, nugae canorae, twaddle, twattle, fudge, trash, garbage, humbug, poppy-cock, stuff, stuff and nonsense, bosh, rubbish, moonshine, wish-wash, fiddle- faddle, absurdity, vagueness, boilerplate, clich_¬, unmeaning, meaningless, senseless, nonsensical, void of sense, inexpressive, unexpressive, vacant, not significant, insignificant, trashy, washy, trumpery, trivial, fiddle-faddle, twaddling, quibbling, unmeant, not expressed, tacit, inexpressible, undefinable, incommunicable.
air letter, airmail letter, black letter, block letter, brain dead, business letter, capital letter, chain letter, commercial letter of credit, cover letter, covering letter, crank letter, dead, dead ahead, dead air, dead axle, dead body, dead center, dead centre, dead drop, dead duck, dead end, dead giveaway, dead hand, dead hand of the past, dead heat, dead language, dead load, dead mail, dead march, dead metaphor, dead nettle, dead of night, dead on target, dead pan, dead person, dead reckoning, dead ringer, dead room, dead sea, dead sea scrolls, dead set, dead shot, dead soul, dead stop, dead tired, dead to, dead to the world, dead weight, drop dead, encyclical letter, fan letter, form letter, investment letter, knock dead, letter, letter a, letter b, letter bomb, letter bond, letter box, letter c, letter carrier, letter case, letter d, letter e, letter f, letter g, letter h, letter i, letter j, letter k, letter l, letter m, letter n, letter o, letter of credit, letter of intent, letter of jeremiah, letter of mark and reprisal, letter of marque, letter of the alphabet, letter opener, letter p, letter paper, letter q, letter r, letter s, letter security, letter stock, letter t, letter telegram, letter u, letter v, letter w, letter writer, letter x, letter y, letter z, living dead, love letter, lower-case letter, market letter, night letter, office of the dead, open letter, personal letter, polyphonic letter, runic letter, scarlet letter, sea letter, short letter, small letter, stop dead, to the letter, traveler's letter of credit, traveller's letter of credit, upper-case letter, varsity letter, white dead nettle