serious-minded

Earlier this year, the two candidates pledged a clean campaign, one that was above the fray, serious-minded.

A more serious-minded direction seems right at first, but then that old, inflated sense of purpose can also lead to bigger damage.

Of course, all of you young ladies are too serious-minded to do such a thing yourselves.

The youth's name proved to be Severne, and he was the most serious-minded youth who had ever stepped from college into writing.

Serious-minded youths never know enough not to believe what a girl says.

Severne took his trouble henceforward in a becomingly serious-minded manner.

So, naturally, he did the obvious thing—that is to say, the obvious thing to a serious-minded writer with no sense of humour.