IPA: /ˈhiːd.fəl.nəs/
KK: /hid-fəl-nəs/
The quality of being careful and paying attention to something important.
Her heedfulness in planning the event ensured that everything went smoothly.
Heedfulness is formed from "heed" (from Old English "hēdan", meaning to take care or pay attention) and "-fulness" (meaning the state of being full of). The word "heedfulness" means the state of being full of care or attention.
Think of 'taking care' ('heed') and being 'full of' that care ('-fulness'). This helps you remember that heedfulness means being attentive and careful.