UK /ˌlɒŋ.ɡɪˈtjuː.dɪ.nəl/ · US /ˌlɔn.dʒɪˈtu.dɪ.nəl/
Etymology From Latin longitūdin- + -al, from oblique stem of Latin longitūdō, from longus + -tūdō. By surface analysis, longitude + -al.
1
Running across a set direction of an object.
The motion about the longitudinal axis of an airplane is called roll.
...forming the bottom of the hopper, in combination with the recriprocating longitudinal movement of the same, for the purpose of regulating the feed from the hopper, substantially as herein set forth.1847, editorial staff, “Winnowing Machines”, in Scientific American, series 1, Volume 3, Issue 9, page 68:
2
Anatomy, Medicine, Sciences Running in the direction of the long axis of a body.
The units have transverse seats, two and three astride the passageway with single or double longitudinal seats alongside the two entrance vestibules in each car.1960 November, “New electric multiple-units for British Railways: Glasgow Suburban”, in Trains Illustrated, page 660:
The third rotation is about the longitudinal axis of the thigh.2008, Youlian Hong, Roger Bartlett, editors, Routledge Handbook of Biomechanics and Human Movement Science, Routledge, →ISBN, page 165:
1 more example
Unlike the older trains, the new units have walk-through carriages and longitudinal rather than transverse seating.2023 February 22, Paul Stephen, “TfL reveals first of new B23s for Docklands Light Railway”, in RAIL, number 977, page 12:
3
Relating to the geographical longitude.
The longitudinal position of a ship refers to its angular distance east or west from the prime meridian.
4
Sciences Of a study, sampling data over time rather than merely once.
longitudinal studies
Examining national longitudinal data, Mossakowski has found that people who were unemployed for long periods in their teens or early 20s are far more likely to develop a habit of heavy drinking (five or more drinks in one sitting) by the time they approach middle age.2010 March 1, Don Peck, “How a New Jobless Era Will Transform America”, in The Atlantic: