lacking in insight or discernment; "too obtuse to grasp the implications of his behavior"; "a purblind oligarchy that flatly refused to see that history was condemning it to the dustbin"- Jasper Griffin
a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return; "sonar is an acronym for sound navigation ranging"; "asdic is an acronym for antisubmarine detection investigation committee"