Noiseless

Holmes had picked up the powerful air-gun from the floor, and was examining its mechanism. "An admirable and unique weapon," said he, "noiseless and of tremendous power."

Source: tatoeba (7453259)

Walking somewhat slowly by reason of his concentration, the boy—an ancient man in some phases of thought, much younger than his years in others—was overtaken by a light-footed pedestrian, whom, notwithstanding the gloom, he could perceive to be wearing an extraordinarily tall hat, a swallow-tailed coat, and a watch-chain that danced madly and threw around scintillations of sky-light as its owner swung along upon a pair of thin legs and noiseless boots.

Source: tatoeba (11477409)

The movements of the cat were noiseless as it approached the mousehole.

Source: wiktionary

For by the hearth the children sit ⁠Cold in that atmosphere of Death, ⁠And scarce endure to draw the breath, Or like to noiseless phantoms flit: But open converse is there none, […]

Source: wiktionary