To display prominently or announce loudly; also, a coat of arms or heraldic shield.
From Old French 'blasoner' meaning to describe arms or heraldry. The verb evolved from heraldic practice where details of shields were publicly announced and displayed. The meaning expanded to describe any prominent public display or announcement.
Medieval heralds literally had to shout descriptions of knights' shields so loudly that 'blazoning' became synonymous with public proclamation—it's why we still use it when someone broadcasts something dramatically.
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