Carelessness

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Old English carlēas ‘free from care’ (see care, -less).

wiktionary

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From Middle English *carelesnes, *carlesnesse, from Old English carlēasnes(“freedom from care, security, carelessness”), equivalent to careless +‎ -ness.

etymonline

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carelessness (n.)

Old English carleasnes "freedom from anxiety;" see careless + -ness. Original sense obsolete. Modern meaning "heedlessness, negligence" (1560s) probably is a fresh formation.