pivotal(s = adj.all) polar - being of crucial importance; "a pivotal event"; "a polar principal"; "Its pivotal location has also exposed it to periodic invasions"; "the polar events of this study"
Derived form noun pivot₁

   Of or pertaining to a pivot or turning point; belonging to, or constituting, a pivot; of the nature of a pivot; as, the pivotalopportunity of a career; the pivotal position in a battle. [1913 Webster]