All 4 Uses

crucial
in
Oryx and Crake
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So many crucial events take place behind people's backs, when they aren't in a position to watch: birth and death, for instance.†
p. 10.9 *

crucial = very important
He said he hadn't kept any crucial information on the home computer she'd wrecked, but of course he would have said that, and there was no way of proving otherwise.†
p. 64.1
He felt he'd disappointed her, he'd failed her in some crucial way.†
p. 68.3
"Kind of is crucial," said Crake.†
p. 292.7

Definitions:

(1) (crucial)
very important or necessary -- often because it determines how something else will turn out
(2) (meaning too rare to warrant focus)