Wiktionary
widthwise
a. directed across the width of an object or place. adv. Across the width of an object or place.
Usage examples of "widthwise".
Had he possessed the sticking power, his books would have swelled, not widthwise across the shelf but downwards, mine-shaft-style.
Spanning this space widthwise were three cross benches, including the one smashed by the zebra.