Gerontology, the branch of medical science which has to do with the processes, physiological and pathological, of extreme old age, or senility.
nos-tol'o-ji, n. the science of the phenomena of extreme old age or senility in which there is ever seen a return to the characteristics of the youthful stage.--adj. NOSTOLOG'IC. [Gr. nostos, return, logia--legein, to speak.]