I. |əltrə+ noun
Etymology: ultra- + sound
: a wave phenomenon of the same physical nature as sound but with frequencies above the range of human hearing — called also supersound
II. noun
1. : the diagnostic or therapeutic use of ultrasound 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 echography sonography
2. : a diagnostic examination using ultrasound