inconsideration

noun

1. (countable, uncountable)Lack of due consideration; inattention to consequences, thoughtlessness.

   “new trained Souldiers, and such as are but novices in the trade, doe often headlong, and hand over head cast themselves into dangers, with more inconsideration, than afterward when they have seene and endured the first shocke, and are better trained in the schoole of perils.”

   “He had no leisure to explain himself further, nor Oriana, prepossessed as she was in favour of Philimore, to weigh the subject with that maturity it demanded:—fatal inconsideration, unbecoming Oriana! Her lover anxiously waiting her reply, she expressed her full consent, when her mother and sister joined her.”