WordWeb Online

1. Not showing due care or attention
   "inattentive students"; "an inattentive babysitter";
   - neglectful, unattentive [rare]
    
2. Showing a lack of attention or care
   "inattentive students"; "an inattentive babysitter";
   - unattentive [rare]

See also: absent, absentminded, abstracted, attention, careless, cavalier, distracted, distrait, dopey, dopy, dreamy, drowsy, forgetful, mindless, moony, negligent, oblivious, oscitant, scatty [Brit, informal], unmindful, woolgathering, yawning

Antonym: attentive