Resounded (6)
'resounded' is the definition.
('echo' can be a synonym of 'resound')
This is the entire clue.
(Other definitions for echoed that I've seen before include "Rang" , "copied" , "said nothing original" , "Repeated a sound" , "Reverberated; repeated" .)
(Another definition for boomed that I've seen is " Made deep resonant sound - or prospered".)