IPA: /ˈhiːdləs/
KK: /ˈhidləs/
Not paying attention or being careless about something.
He was heedless of the warning signs on the road.
Comparative: more heedless
Superlative: most heedless
Heedless is formed from "heed" (from Old English *hēdan*, meaning to take care or pay attention) and "-less" (meaning without). The word describes a state of being without care or attention.
Think of 'heed' as paying attention, and remember that 'heedless' means being without attention or care.