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"
(of persons) freed from or not subject to an obligation or liability (as e.g. taxes) to which others or other things are subject; "a beauty somehow exempt from the aging process"; "exempt from jury duty"; "only the very poorest citizens should be exempt from income taxes"
grant relief or an exemption from a rule or requirement to; "She exempted me from the exam"