Showdown
/noun UK /ˈʃəʊ.daʊn/ US /ˈʃoʊ.daʊn
an important argument that is intended to end a disagreement that has existed for a long time
Example. The president is preparing for a showdown with Republicans over his plans to reform the economy
Millions of dollars were spent on lawyers in a courtroom showdown between the two companies
Synonym: confrontation