death blow at English => English (Longman) Of Explained:
n [singular] an action or event that makes something fail or end// death knell// --His decision to leave the show has delivered a death blow to the series.//
death blow at English => English (Oxford Advanced Learners) Of Explained:
an event that destroys or puts an end to sth:
They thought the arrival of television would deal a death blow to mass cinema audiences.