Douglas Harper's Etymology Dictionary
Wiktionary
a. 1 (context of sound waves acoustics English) Having frequencies below the human audible range 2 (context of a device English) Generating or employing such sound waves
WordNet
adj. having frequencies below those of audible sound
Usage examples of "infrasonic".
She was swimming out through layers of life, and she sensed the subtle sounds of living things washing through the sphere: the smooth rush of the fish as they swam in their tight schools, the bubbling murmur of the krill on which they browsed, the hiss of the diatoms and algae that fed them, and the deep infrasonic rumble of the water itself, compression waves pulsing through its bulk.
He reset his infrasonic cutter and made a second slice, cropped it, sang again, tuned the cutter, and dug the blade in six neat slashes downward.
He inspected every part of the device, even unsheathing the infrasonic blade, which he gave the keenest scrutiny.
The staircase that leads over the tracks to Utter Maurby Terminal is enclosed with roof and walls, forming a gigantic organ pipe that resonates with an infrasonic throb as it is pummeled by wind and water.
She gave a little gasp as she saw that her name had been incised in neat letters on the plas housing that covered the infrasonic blade.