1. 
2. 
[syn: lengthways, lengthwise, longwise, longways, longitudinally]
3.  with respect to longitude; 
- Example: "longitudinally measured"
The Collaborative International Dictionary of English v.0.48:
Longitudinally \Lon`gi*tu"di*nal*ly\, adv.
   In the direction of length.
   [1913 Webster]
WordNet (r) 3.0 (2006):
longitudinally
    adv 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,
       longitudinally]
    3: with respect to longitude; "longitudinally measured"