Paying close attention and giving careful consideration to something.
From 'heed' plus the adjective suffix '-ful' meaning full of; originally meant 'full of regard or care for.'
Heedful is an old-fashioned word that appears constantly in 19th-century literature, but we've mostly replaced it with 'mindful' or 'attentive'—language evolves as old words feel too formal or stuffy.
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