ADJECTIVE (3)

1. of or relating to lines of longitude;
- Example: "longitudinal reckoning by the navigator"

2. running lengthwise;
- Example: "a thin longitudinal strip"
- Example: "longitudinal measurements of the hull"

3. over an extended time;
- Example: "a longitudinal study of twins"

The Collaborative International Dictionary of English v.0.48:

Longitudinal \Lon`gi*tu"di*nal\, a. [Cf. F. longitudinal.]
   1. Of or pertaining to longitude or length; as, longitudinal
      distance.
      [1913 Webster]

   2. Extending in length; in the direction of the length;
      running lengthwise, as distinguished from transverse;
      as, the longitudinal diameter of a body. --Cheyne.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Longitudinal \Lon`gi*tu"di*nal\, n.
   A railway sleeper lying parallel with the rail.
   [1913 Webster]

WordNet (r) 3.0 (2006):

longitudinal
    adj 1: of or relating to lines of longitude; "longitudinal
           reckoning by the navigator"
    2: running lengthwise; "a thin longitudinal strip";
       "longitudinal measurements of the hull"
    3: over an extended time; "a longitudinal study of twins"