adjective. Generating or using waves or vibrations with frequencies below that of audible sound.

adjective. Having frequencies below the human audible range

adjective. Generating or employing such sound waves

adjective. having frequencies below those of audible sound

"However, technological advances are making it possible to develop WMD based on qualitatively new principles, such as infrasonic (acoustic), radiological (enhanced-radiation), or particle-beam weapons."