Here sat Marilla Cuthbert, when she sat at all, always slightly distrustful of sunshine, which seemed to her too dancing and irresponsible a thing for a world which was meant to be taken seriously; and here she sat now, knitting, and the table behind her was laid for supper.
There are no more uses of "irresponsible" in the book.
Show samples from other sources
After much passing around of money Cousin Joshua was moved across the tracks and placed in state accommodations for the irresponsible, where he remained for the rest of his days.
Harper Lee -- Go Set a Watchman
"The fact of the matter is, we’ve been irresponsible," Marybeth continues.