In a fundamental, extreme, or revolutionary way that changes things completely.
From Latin 'radicalis' meaning 'of or going to the root,' derived from 'radix' (root). The adverb form emphasizes doing something at the root level rather than superficially.
When something changes 'radically,' it means you're pulling it up by the roots and replanting it entirely—which is why social movements and scientific revolutions are called radical, because they reorganize foundations rather than just fixing surfaces.
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