Things that are completely different from each other or as different as possible, like hot and cold or day and night.
From Latin 'oppositus,' past participle of 'opponere' (to set against), composed of 'ob-' (against) and 'ponere' (to place). The meaning literally describes things placed against each other.
Your brain finds opposites weirdly useful—they help you understand concepts faster because the contrast makes meaning pop out, which is why kids learn 'big' and 'small' together.
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