Superlative form of blunt: the most dull or least sharp; the most direct and frank in manner.
From 'blunt' plus the superlative suffix '-est,' which indicates the greatest degree. This is the standard way English marks the highest level of a quality.
The superlative 'bluntest' is actually rarer in speech than the comparative 'blunter'—people find it easier to compare two things than to declare something the absolute most of anything.
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