Lewis & Short

ad-algĭdus, a, um, adj. [ad, intens.], very cold, chilly; of climate: adalgidum maxime, Fronto, Ep. ad M. Caes. 2, 9, p. 54 Mai; in Naev. ap. Cic. Or. 45, 152, Clussman would read adalgidum for atque algidum (B. and K.).