Said or done without stopping to think first, especially without thinking about what might happen afterwards. If you make an unconsidered remark, you did not weigh your words — you just said them, and someone may get hurt or you may look foolish. It is a quiet, slightly formal word; it does not shout at the person the way 'careless' or 'stupid' would, but it is still a criticism. Notice that it usually goes in front of a noun: unconsidered remarks, an unconsidered decision, unconsidered action. You almost never say 'his remark was unconsidered' — that sounds odd. There is a second, older use that you will meet in reading: 'unconsidered' can mean 'not looked at, not taken into account' — an unconsidered factor is one nobody thought about, and here nobody is being blamed at all. Shakespeare fans know the phrase 'a snapper-up of unconsidered trifles', where it means small things nobody bothered to value. So the same word can point at the speaker (you didn't think) or at the thing (nobody noticed it); the sentence tells you which.