heedlessness vs inattention

heedlessness and inattention both are nouns.

Word	Noun	Adjective	Verb	Adverb
heedlessness	Yes	No	No	No
inattention	Yes	No	No	No

As nouns, inattention is a hypernym of heedlessness; that is, inattention is a word with a broader meaning than heedlessness:

heedlessness (noun)	inattention (noun)
the trait of forgetting or ignoring your responsibilities	lack of attention
the trait of acting rashly and without prudence
a lack of attentiveness (as to children or helpless people)