From side to side; across.
Above, the stars appeared to move slowly athwart.
Across the path (of something).
a fleet standing athwart our course
Wrongly; perplexingly.
From one side to the other side of.
The stars moved slowly athwart the sky.
Across the line of a ship's course or across its deck.
The damaged mainmast fell athwart the deck, destroying the ship's boat.
Across the path or course of; opposing.