Pronunciation: (lon"ji-tOOd'n-l, -tyOOd'-),[key] —adj. 1. of or pertaining to longitude or length: longitudinal measurement. 2. extending in the direction of the length of a thing; running lengthwise: a thin, longitudinal stripe. 3. Zool.pertaining to or extending along the long axis of the body, or the direction from front to back, or head to tail.
4. pertaining to a research design or survey in which the same subjects are observed repeatedly over a period of time.
—n. a longitudinal framing member, as in the hull of a ship.