obnoxious Look up obnoxious at Dictionary.com
1581, from L. obnoxiosus "hurtful, injurious," from obnoxius "subject to harm," from ob "to, toward" + noxa "injury, hurt, damage entailing liability" (see noxious). Originally "subject to authority, subject to something harmful;" meaning "offensive, hateful" is first recorded 1675, influenced by noxious (q.v.).
"Obnoxious has two very different senses, one of which (exposed or open or liable to attack or injury) requires notice because its currency is now so restricted that it is puzzling to the uninstructed. It is the word's rightful or de jure meaning, and we may hope that scholarly writers will keep it alive." [Fowler]