Adjective
Not perceptible; not to be apprehended or cognized by the souses; not discernible by the mind; not easily apprehended.
Source: Webster's dictionaryAll the great and beneficent operations of Nature are produced by slow and often imperceptible degrees. The work of destruction and devastation only is violent and rapid. Albert Pike
Man is an imperceptible atom always trying to become one with God. Henry Adams
These joys were so trifling as to be as imperceptible as grains of gold among the sand, and in moments of depression she saw nothing but the sand; yet there were brighter moments when she felt nothing but joy, saw nothing but the gold. Leo Tolstoy
Nobody wants a girl whose beauty is imperceptible to all but him... Germaine Greer
God works in a mysterious way in grace as well as in nature, concealing His operations under an imperceptible succession of events, and thus keeps us always in the darkness of faith. François Fénelon
[Contagion] passes from one thing to another, and is originally caused by infection of the imperceptible particle. Fracastorius