1 across time; "We studied the development of the children longitudinally"
2 in the direction of the length; "He cut the paper lengthwise" [syn: lengthways, lengthwise, longwise, longways]
3 with respect to longitude; "longitudinally measured"
The term, longitudinal means "along the major (or long) axis" as opposed to latitudinal which means "along the width", transverse, or across.
See also: longitude