Wordnet 3.0
NOUN (1)
1. 
 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; 
- Example: "sonar is an acronym for sound navigation ranging"- Example: "asdic is an acronym for antisubmarine detection investigation committee"[syn: sonar, echo sounder, asdic]
WordNet (r) 3.0 (2006):
echo sounder
    n 1: 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" [syn: sonar, echo
         sounder, asdic]