lon ‧ gi ‧ tu ‧ di ‧ nal /ˌlɒndʒəˈtjuːdən ə l◂, ˌlɒndʒɪˈtjuːdən ə l◂ $ ˌlɑːndʒəˈtuː-/ BrE AmE adjective technical
1 . relating to the development of something over a period of time
longitudinal study/survey/research etc
a longitudinal study of unemployed workers
2 . going from top to bottom, not across:
longitudinal stripes
3 . measured according to longitude
—longitudinally adverb