cardinal
Reveal answer
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cardinal
self-satisfied
award of merit
chief
(of air) thin in density
"Cardinal" means most important, fundamental, or chief (e.g., "cardinal sins," "cardinal directions"). Option A "self-satisfied" is incorrect (that's "complacent"). Option B "award of merit" is wrong (that's "prize"). Option D "thin in density" is also incorrect (that's "rarefied").