Impossible or difficult to perceive by the mind or senses:
— An imperceptible drop in temperature.
— An imperceptible nod.

synonym: unperceivable.

Roget 275: slow, slack; tardy; dilatory etc. (inactive) 683; gentle, easy; leisurely; deliberate, gradual; insensible, imperceptible; glacial, languid, sluggish, slow paced, tardigrade^†, snail-like; creeping etc. v.; reptatorial^†.    ... show more

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

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

Dutch: onmerkbaar