IPA: /ˌɪnəˈtɛn.tɪv.nəs/
KK: /ɪnəˈtɛntɪvnəs/
The quality of not paying attention or being careless in focus.
His inattentiveness during the lecture caused him to miss important information.
Inattentiveness → It is formed from "in-" (meaning not), "attentus" (from Latin "attendere", meaning to stretch toward or pay attention), and "-ness" (meaning the state of being). The word describes the state of not paying attention or being distracted.
Think of 'not' ('in-') paying attention ('attendere') — that's what inattentiveness means.