When you do something venally, you do it in an underhanded, dishonest way. If you made a lot of money venally, you might want to consider giving it back.
The adverb venally is perfect for describing something done in a sneaky or corrupt way. Big banks are often accused of acting venally, as are many politicians and other public figures. If you hurt someone who's weaker than you are or pay someone to write your English essay, you're also behaving venally. The adjective venal is at the root of venally, with its original meaning of "capable of being obtained for a price," and its Latin origin, venum, "for sale."