rash; thoughtless; careless; hasty
Example sentences
彼は頭はよいが、他方ではしばしば軽率な間違いをする。
He is clever, but on the other hand he often makes careless mistakes.
彼は軽率だという評判だった。
He had a reputation for carelessness.
控え目に言っても彼はちょっと軽率だった。
He was rather careless to say the least.