Lewis & Short

mortŭrĭo, ire, 4, v. n. desid. [mors], to long for death, desire to die: dictum est a Cicerone de philosophis, morturiunt, mori desiderant, Aug. de Gram. p: 2006 P. (Cic. Fragm. 50, 29, p. 146 B. and K.).