The Collaborative International Dictionary
Inobservant
Inobservant \In`ob*serv"ant\, a. [L. inobservans. See In- not,
and Observant.]
Not observant; regardless; heedless.
--Bp. Hurd. --
In`ob*serv"ant*ly, adv.
Douglas Harper's Etymology Dictionary
inobservant
1660s, from Latin inobservantem (nominative inobservans) "inattentive, negligent," from in- "not" (see in- (1)) + observans (see observance).\n
Wiktionary
inobservant
a. Not observant; heedless.