imperceptible

The hum of the electric motor is imperceptible, and it is only at speed that the sound of the rolling wheels on the road breaks through.

Five years later, Mini sat on Khorram’s lap, her disability nearly imperceptible — and in any case eclipsed by her purple-dyed tail.

Though the evidence may be imperceptible to the untrained eye, they also hold the memory of the earth from which they were formed and the traditional methods of molding and firing clay.

The shrewd, vivifying juxtaposition pits crude, primal, static stone, its huge weight pressing the ground beneath your feet, against sleek, industrially elegant windmills spinning overhead to catch the invisible airstream and generate similarly imperceptible energy.

Richards, also known as Mister Fantastic, has the ability to stretch his body to the extreme, while his partner, Sue — a.k.a. the Invisible Woman — is imperceptible and can manipulate force fields.