Comparative form of careful: more careful, showing greater attention to detail or greater caution than something else.
From careful + -er (comparative suffix). An older or dialectal comparative form, as modern English typically uses 'more careful' rather than 'carefuller.'
Words like 'carefuller' show English in transition—historically people said 'carefuller,' but modern English prefers 'more careful,' and this shift reveals how English is gradually standardizing on the 'more' + adjective pattern for longer words.
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