In a way that is overwhelming, oppressive, or psychologically devastating; to an overwhelming degree.
From crushing (crush + -ing) plus -ly to make an adverb. The metaphorical meaning of 'overwhelming pressure' developed from the literal meaning of crush.
When someone loses an election with 'crushingly' low vote numbers or gets 'crushingly' bad reviews, the word carries the physical sensation of pressure—like the weight is actually pressing down on you.
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