Merriam-Webster Collegiate Dictionary - ultrasound

 noun  Date: 1923  1. vibrations of the same physical nature as sound but with frequencies above the range of human hearing  2. the diagnostic or therapeutic use of ~ and especially a noninvasive technique involving the formation of a two-dimensional image used for the examination and measurement of internal body structures and the detection of bodily abnormalities — called also sonography  3. a diagnostic examination using ~