Explosion (4)
'explosion' is the definition.
(blast is a kind of explosion)
This is all the clue.
(Other definitions for blast that I've seen before include "Severe reprimand; strong gust" , "Blow up or swear" , "Loud horn sound" , "slate" , "Effect of explosion" .)
'explosion' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for boom that I've seen before include "it sometimes accompanies 19 [BABY]" , "Horizontal spar on board" , "(Make a) loud noise" , "It may protect harbour" , "Harbour barrier" .)