Smugness faded from it, replaced by a dogged earnestness that fooled Judge Taylor not at all: as long as Mr. Ewell was on the stand, the judge kept his eyes on him, as if daring him to make a false move.
There are no more uses of "earnest" in the book.
Show samples from other sources
Both sides were deeply in earnest, even passionate.
She has a casual, go-with-the-flow personality and doesn’t appreciate his earnestness.