[mass noun]a system for the detection of objects under water by emitting sound pulses and detecting or measuring their return after being reflected 声呐 ■[count noun]an apparatus used in this system 声波定位仪 ■the method of echolocation used in air or water by animals such as whales and bats 声呐定位法
语源
1940s: from so(und) na(vigation and) r(anging), on the pattern of radar