longitudinal
1. [ adjective ] running lengthwise
Examples:

"a thin longitudinal strip" "longitudinal measurements of the hull"

Related terms: lengthwise
2. [ adjective ] of or relating to lines of longitude
Examples:

"longitudinal reckoning by the navigator"

Related terms: meridian
3. [ adjective ] over an extended time
Examples:

"a longitudinal study of twins"

Related terms: long
Similar spelling:   longitudinally
  longitude
  longstanding