PIVOTAL
pivotal, polar
(adjective) 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”
Source: WordNet® 3.1
Etymology
Adjective
pivotal (comparative more pivotal, superlative most pivotal)
Of, relating to, or being a pivot.
Being of crucial importance; central, key.
Source: Wiktionary
Piv"ot*al, a.
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition