A strong, harsh light that's uncomfortable to look at; or to look angrily at someone with an intense stare.
From Middle English 'glaren,' possibly from Old Norse 'glarr' meaning 'to gleam.' The harsh stare meaning developed from the intensity of looking as intensely as a bright light.
Sunglasses were originally invented in China and then 18th-century Venice to reduce glare, but then they became cool—so eventually we wore them because we wanted to look mysterious, not because we needed them!
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