ultrasound /ul″trəsound/ [L, ultra + sonus] , 1. sound waves at the very high frequency of over 20 kHz (vibrations per second). Ultrasound has many medical applications, including fetal monitoring, imaging of internal organs, and, at an extremely high frequency, the cleaning of dental and surgical instruments. −ultrasonic, adj. 2. the image taken by an ultrasound machine.
