Synonyms:
pivotal, polar
Meaning: being of crucial importance; "a pivotal event"; "Its pivotal location has also exposed it to periodic invasions"- Henry Kissinger; "the polar events of this study"; "a polar principal"
Usage examples
For instance, in the Presidential election of 1868, General Grant, the Republican candidate, lost the important and pivotal State of New York, a loss which would have resulted in his defeat if the Southern States that took part in that election had all voted against him.