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"
call to remembrance; keep alive the memory of someone or something, as in a ceremony; "We remembered the 50th anniversary of the liberation of Auschwitz"; "Remember the dead of the First World War"
be or provide a memorial to a person or an event; "This sculpture commemorates the victims of the concentration camps"; "We memorialized the Dead"
mark by some ceremony or observation; "We marked the anniversary of his death"