Resonance (4)
(Other definitions for boom that I've seen before include "Time of great prosperity - hear the sound" , "time of 22 [PROSPERITY]" , "Spar - loud noise" , "Prosperous time - sound of explosion - yachting spar" , "Period of prosperity or sonic sound" .)
'resonance' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for vibration that I've seen before include "Palpitation, oscillation" , "fast pulse?" , "Quick back and forward movement" , "Rapid to-and-fro motion" , "Oscillating movement" .)