The superlative form of 'grave,' meaning most serious, most solemn, or most threatening.
From Old English 'graf' or Old French 'grave' (heavy, weighty), from Latin 'gravis' (heavy). The superlative 'gravest' adds the suffix '-est' to mean 'most.'
The word 'grave' has two meanings—serious/solemn AND a burial place—and they both come from the same Latin root 'gravis' (heavy), because things that are heavy in weight and heavy in importance both seemed important to ancient people.
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