also: まんらん
na-adjective, noun
careless; sloppy; incoherent; negligent
Rare literary word describing careless, incoherent, or negligent behavior or speech. Not used in everyday conversation.
彼の孟浪な態度には呆れてしまった。
I was appalled by his careless attitude.
その文章は孟浪で、何を言いたいのかわからない
The writing is incoherent; I can't tell what it's trying to say.
The exact derivation is uncertain; the kanji 孟 (beginning, chief) and 浪 (wave, wandering) are used here in a conventional literary sense to convey carelessness or incoherence, possibly of Chinese origin.