Turned into a fossil (the preserved remains of an ancient organism), or figuratively, something that has become old-fashioned and unchanging.
From fossil (from Latin fossilis meaning 'dug up') + -ize (to make or become) + -d (past tense/adjective form). The word emerged in English to describe the geological process, then metaphorically extended to describe anything rigidly fixed in old patterns.
The metaphorical use is brilliant—when we call an idea 'fossilised,' we're saying it's so old it's basically dead and preserved, which is way more vivid than just saying 'outdated,' and it unconsciously links resistant thinking to extinction.
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