Shut forcefully and loudly; also criticized harshly or struck with great force.
From Middle English slammen, of uncertain origin, possibly imitative of the sound made by forceful closing. The word has been in English since the 17th century, with the metaphorical sense of harsh criticism developing in the 20th century.
Slammed is a perfect example of onomatopoeia - the word sounds like what it describes, that sharp, final crack of something closing with force. It's fascinating how we've extended this physical sound to describe verbal attacks, as if harsh criticism makes the same kind of jarring noise in our minds.
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