pivotal
PIV-uh-tuladjMeaning of central importance; the point on which everything turns
Memory hook PIVOT-al: everything TURNS on it. The whole seesaw tips up and down on one little pin in the middle. Without it, nothing moves: the pin is pivotal.
Winning the coin toss turned out to be pivotal in the close game.
In context Meeting her chemistry teacher was a pivotal moment in Ada’s life; before that, she had never thought about science, and afterward she could think of little else.
Similar central, key, critical, crucial
Opposite minor, peripheral, unimportant
From pivot, the pin or point on which something turns.