IPA: /ˈhiːd.ləs.li/
KK: /ˈhidlɪsli/
In a way that shows a lack of care or attention to something important.
He drove heedlessly through the busy streets, ignoring the traffic signals.
Heedlessly → It is formed from "heed" (from Old English *hēdan*, meaning to take care or pay attention) and the suffix "-less" (meaning without). The word "heedlessly" means without paying attention or care.
Think of 'heed' as taking care or paying attention, and remember that 'heedlessly' means doing something without that care.