Lewis & Short

pĕrennĭtas, ātis, f. [perennis], lastingness, continuance, perpetual duration, perpetuity (class.): fontium perennitates, Cic. N. D. 2, 39, 98: cibi, constant food, Plaut. Pers. 3, 1, 2: perennitatem conditis frumentis afferunt, Col. 1, 6, 10: vitae, Ambros. in Psa. 118, Serm. 13, 22: Perennitas, a title of the Roman emperors: vestra, your perpetuity, your perennity, Symm. Ep. 10, 45; Sex. Ruf. Brev. 2.