Imperceptible

Adjective

 * 1) Not perceptible, not detectable, too small in magnitude to be observed.
 * We all missed the imperceptible shake of his head as he tried to warn us without being seen.

Adverbs for Imperceptible
altogether; definitely; materially; infinitesi- mally; miserably; comparatively; almost; unaccountably; impalpably; evanescently; nebulously; vaporously; obscurely; fuzzily; curiously; symbolically; inferentially; covertly.

Thesaurus
atomic, behind the curtain, behind the scenes, camouflaged, concealed, corpuscular, disguised, embryonic, ephemeral, evanescent, faint, fugitive, germinal, granular, hidden, ill-defined, impalpable, imponderable, inappreciable, inaudible, inconsiderable, inconspicuous, indiscernible, indistinct, indistinguishable, infinitesimal, insensible, insignificant, intangible, invisible, latent, microcosmic, microscopic, minuscule, minute, molecular, momentary, obscure, out of sight, secret, sightless, slight, subatomic, submerged, subtle, tenuous, thin, tiny, trivial, ultramicroscopic, unapparent, unappreciable, unbeheld, unbeholdable, unclear, undiscernible, undistinguishable, unnoticeable, unnoticed, unobservable, unobserved, unperceivable, unperceived, unrealized, unseeable, unseen, unviewed, unwitnessed, vague, viewless

Etymology
, from, from imperceptibilis:

Translations

 * French:

Etymology
From the imperceptibilis:.