- The word come from the Latin longitudo meaning length. Hence, longitudinal means along the length, running lengthwise, or (by extension) over the course of time.
* * *1. Running lengthwise; in the direction of the long axis of the body or any of its parts. SYN: longitudinalis [TA]. 2. Studied over a period of time, diachronic; contrast with cross-sectional or synchronic, which give equivalent results only under certain strict conditions of stability and equilibrium. Strict attention to these conditions is of the greatest importance in the study of survivorship either in demographics or in cell economy (such as the survival pattern of the erythrocytes and platelets). [L. longitudo, length]
* * *1) of, relating to, or occurring in the lengthwise dimension <a \longitudinal bone fracture>2) extending along or relating to the anteroposterior axis of a body or part <a trypanosome which reproduces by \longitudinal fission>3) involving the repeated observation or examination of a set of subjects over time with respect to one or more study variables (as general health, the state of a disease, or mortality) <a \longitudinal study of heart transplant recipients over a five-year period>lon·gi·tu·di·nal·ly -ē adv
* * *lon·gi·tu·di·nal (lon″jĭ-tooґdi-nəl) [L. longitudo length] lengthwise; parallel to the long axis of the body or an organ.
Medical dictionary. 2011.