... taking case that contains new boom (4)
I believe the answer is:
bang
'boom' is the definition.
(thesaurus)
'taking case that contains new' is the wordplay.
'taking case' becomes 'bag' (bag is a kind of case. I am not sure about the 'taking' bit.).
'that contains' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'bag' going around 'n' is 'BANG'.
Can you help me to learn more?
(Other definitions for bang that I've seen before include "Strike violently" , "Sudden loud noise like an explosion" , "precisely" , "Completely modern" , "Sudden noise; fringe" .)