Definitions

1. adverb

in the direction of length or in a direction parallel to the length of something

“Cut the log lengthwise into planks.”

2. adverb

from end to end or in the direction of the length of something

“The parade marched lengthwise down Main Street.”

3. noun

the direction or orientation of something in relation to its length

“The instructions specified the lengthwise orientation of the furniture in the room.”