Amtrak, Charley, L, Trojan horse, VC, Vietcong, abstruse, agreement to disagree, alienated, alienation, alternative, antiestablishment, apostasy, at odds with, at rest, at variance with, avant-garde, back door, back stairs, back way, back-door, backstairs, baggage train, beclouded, behind the curtain, behind the scenes, behind the veil, blind, bolt-hole, branch, breakaway, buried, bushfighter, bushwhacker, cable railroad, cable railway, casual, choo-choo, clandestine, close, clouded, cog railroad, cog railway, collaborationist, collaborator, concealed, counter-culture, covered, covert, covert way, covertly, crypto, deep-buried, difference, differing, disaccord, disagreeing, disagreement, disapprobation, disapproval, disparity, dissatisfaction, dissension, dissent, dissentience, dissentient, dissenting, dissidence, dissident, diversity, dropping out, eclipsed, el, electric, electric railway, electric train, elevated, elevated railway, embankment, escalier derobe, escape hatch, escape route, experimental, express, express train, extremists, feeder, feeder line, feline, fellow traveler, fifth column, fifth columnist, flier, fraternizer, freight, freight train, freighter, funicular, furtive, goods train, gravity-operated railway, guerillas, guerrilla, hid, hidden, hidlings, hole-and-corner, horse railway, hugger-mugger, in a cloud, in a corner, in a fog, in a whisper, in darkness, in eclipse, in hidlings, in opposition, in purdah, in secret, in the background, in the dark, in the wings, incommunicado, insurgents, insurrectionists, interurban, irregular, junction, latent, light railroad, lightning express, limited, line, local, main line, maquis, maquisard, metro, milk train, minority opinion, monorail, mysterious, nobody the wiser, nonagreement, nonassent, nonconcurrence, nonconforming, nonconformist, nonconformity, nonconsent, obfuscated, obscure, obscured, occult, opposing, opposition, parliamentary, parliamentary train, partisan, passenger train, private, privy, quiet, rack railway, rack-and-pinion railroad, rack-and-pinion railway, radical, rail, rail line, railroad, railroad train, railway, rattler, recondite, recusance, recusancy, recusant, rejection, repudiation, resistance, resistance fighter, resting in peace, revolutionary, roadbed, roadway, rolling stock, saboteur, secession, secluded, secluse, secret, secret exit, secret passage, secret staircase, secretly, sectarian, sectary, security risk, sequestered, shifty, shuttle, shuttle train, side door, sidetrack, siding, skulking, slinking, slinky, sly, sneaking, sneaky, sotto voce, special, stealthy, streamliner, street railway, streetcar line, sub rosa, subterranean, subterraneous, subversive, subversives, subway, sunken, surreptitious, switchback, terminal, terminus, track, train, tram, tramline, trestle, trolley line, trunk, trunk line, tube, turnout, under an eclipse, under cover, under house arrest, under the breath, under the rose, under wraps, under-the-counter, under-the-table, undercover, underfoot, underground
route, underhand, underhanded, unknown, unobtrusive, variance, way train, with bated breath, withdrawal, wrapped in clouds
depth, deepness, profundity, depression, hollow, pit, shaft, well, crater, gulf, bowels of the earth, botttomless pit, hell, soundings, depth of water, water, draught, submersion, plummet, sound, probe, sounding rod, sounding line, lead, bathymetry, sonar, side-looking sonar, bathometer, deep, deep seated, profound, sunk, buried, submerged, subaqueous, submarine, subterranean, subterraneous, subterrene, underground
, bottomless, soundless, fathomless, unfathomed, unfathomable, abysmal, deep as a well, bathycolpian, benthal, benthopelagic, downreaching, yawning, knee deep, ankle deep, beyond one's depth, out of one's depth, over head and ears, mark twine, mark twain.
latency, implication, latency, inexpression, hidden meaning, occult meaning, occultness, mystery, cabala, anagoge, silence, concealment, more than meets the eye, more than meets the ear, Delphic oracle, le dessous des cartes, undercurrent, implication, logical implication, logical consequence, entailment, allusion, insinuation, innuendo, adumbration, something rotten in the state of Denmark, snake in the grass, secret, darkness, invisibility, imperceptibility, latent, lurking, secret, occult, implied, dormant, abeyant, unapparent, unknown, unseen, in the background, invisible, indiscoverable, dark, impenetrable, unspied, unsuspected, unsaid, unwritten, unpublished, unbreathed, untalked of, untold &c, unsung, unexposed, unproclaimed, undisclosed, unexpressed, not expressed, tacit, undeveloped, solved, unexplained, untraced, undiscovered, untracked, unexplored, uninvented, indirect, crooked, inferential, by inference, by implication, implicit, constructive, allusive, covert, muffled, steganographic, understood, underhand, underground
, delitescent, concealed, by a side wind, sub silentio, in the background, behind the scenes, behind one's back, on the tip of one's tongue, secretly, between the lines, thereby hangs a tale, tacitum vivit sub pectore vulnus, where there's smoke, there's fire.
concealment, hiding, occultation, mystification, seal of secrecy, screen, disguise, masquerade, masked battery, hiding place, cryptography, steganography, freemasonry, stealth, stealthiness, sneakiness, obreption, slyness, latitancy, latitation, seclusion, privacy, secrecy, secretness, incognita, reticence, reserve, mental reserve, reservation, arriere pensee, suppression, evasion, white lie, misprision, silence, suppression of truth, underhand dealing, closeness, secretiveness, mystery, latency, snake in the grass, secret, stowaway, concealed, hidden, secret, recondite, mystic, cabalistic, occult, dark, cryptic, cryptical, private, privy, in petto, auricular, clandestine, close, inviolate, tortuous, behind a screen, undercover, under an eclipse, in ambush, in hiding, in disguise, in a cloud, in a fog, in a mist, in a haze, in a dark corner, in the shade, in the dark, clouded, wrapped in clouds, wrapt in clouds, invisible, buried, underground
, perdu, secluded, undisclosed &c, untold, covert, untraceable, mysterious, irrevealable, inviolable, confidential, esoteric, not to be spoken of, unmentionable, obreptitious, furtive, stealthy, feline, skulking, surreptitious, underhand, hole and corner, sly, secretive, evasive, reserved, reticent, uncommunicative, buttoned up, close, close as wax, taciturn, secretly, in secret, in private, in one's sleeve, in holes and corners, in the dark, januis clausis, with closed doors, a huis clos, hugger mugger, a la derobee, under the cloak of, under the rose, under the table, sub rosa, en tapinois, in the background, aside, on the sly, with bated breath, sotto voce, in a whisper, without beat of drum, a la sourdine, behind the veil, beyond mortal ken, beyond the grave, beyond the veil, hid from mortal vision, into the eternal secret, into the realms supersensible, into the supreme mystery, in confidence, in strict confidence, in strictest confidence, confidentially, between ourselves, between you and me, between you and me and the bedpost, entre nous, inter nos, under the seal of secrecy, a couvert, underhand, by stealth, like a thief in the night, stealthily, behind the scenes, behind the curtain, behind one's back, behind a screen, incognito, in camera, it must go no further, it will go no further, don't tell a soul, tell it not in Gath, nobody the wiser, alitur vitium vivitque tegendo, let it be tenable in your silence still, background information, deep background information, deep background, background session, backgrounder, not for attribution.