Impossible or nearly impossible to see; imperceptible by the eye:
— The invisible man.
— Invisible rays.
— An invisible hinge.
— Invisible mending.

synonym: unseeable.

Roget 526: latent; lurking etc. v.; secret etc. 528; occult; implied etc. v.; dormant; abeyant.    unapparent, unknown, unseen etc. 441; in the background; invisible etc. 447; indiscoverable^†, dark; impenetrable etc. (unintelligible) 519; unspied^†, unsuspected.    unsaid, unwritten, unpublished, unbreathed^†, untalked of^†, untold etc. 527, unsung, unexposed, unproclaimed^†, undisclosed etc. 529, unexpressed; not expressed, tacit.    undeveloped, solved, unexplained, untraced^†, undiscovered etc. 480.1, untracked, unexplored, uninvented^†.    indirect, crooked, inferential; by inference, by implication; implicit; constructive; allusive, covert, muffled; steganographic^†; understood, underhand, underground; delitescent^†, concealed etc. 528.    ... show more

Roget 193: little; small etc. (in quantity) 32; minute, diminutive, microscopic; microzoal; inconsiderable etc. (unimportant) 643; exiguous, puny, tiny, wee, petty, minikin^†, miniature, pygmy, pigmy^†, elfin; undersized; dwarf, dwarfed, dwarfish; spare, stunted, limited; cramp, cramped; pollard, Liliputian, dapper, pocket; portative^†, portable; duodecimo^†; dumpy, squat; short etc. 201.    impalpable, intangible, evanescent, imperceptible, invisible, inappreciable, insignificant, inconsiderable, trivial; infinitesimal, homoeopathic^†; atomic, subatomic, corpuscular, molecular; rudimentary, rudimental; embryonic, vestigial.    weazen^†, scant, scraggy, scrubby; thin etc. (narrow) 203; granular etc. (powdery) 330; shrunk etc. 195; brevipennate^†.    ... show more

Roget 528: concealed etc. v.; hidden; secret, recondite, mystic, cabalistic, occult, dark; cryptic, cryptical^†; private, privy, in petto, auricular, clandestine, close, inviolate; tortuous.    behind a screen etc. 530; 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 etc. 447; buried, underground, perdu [Fr.]; secluded etc. 893.    undisclosed etc. 529, untold etc. 527; covert etc. (latent) 526; untraceable; mysterious etc. (unintelligible) 519.    irrevealable^†, inviolable; confidential; esoteric; not to be spoken of; unmentionable.    obreptitious^†, furtive, stealthy, feline; skulking etc. v.; surreptitious, underhand, hole and corner; sly etc. (cunning) 702; secretive, evasive; reserved, reticent, uncommunicative, buttoned up; close, close as wax; taciturn etc. 585.    ... show more

Polish: niewidzialny, niewidoczny

Not prominent or readily noticeable:
— The invisible man.

synonym: inconspicuous.

Roget 447: invisible, imperceptible; undiscernible^†, indiscernible; unapparent, non-apparent; out of sight, not in sight; a perte de vue [Fr.]; behind the scenes, behind the curtain; viewless, sightless; inconspicuous, unconspicuous^†; unseen etc. (see) etc. 441; covert etc. (latent) 526; eclipsed, under an eclipse.    dim etc. (faint) 422; mysterious, dark, obscure, confused; indistinct, indistinguishable; shadowy, indefinite, undefined; ill-defined, ill-marked; blurred, fuzzy, out of focus; misty etc. (opaque) 426; delitescent^†.    hidden, obscured, covered, veiled (concealed) 528.    ... show more

Dutch: onopvallend