Lewis & Short

chrŏnĭcus, a, um, adj., = χρονικός, pertaining to time: libri, chronicles, Gell. 17, 21, 1; so also absol.: chrŏnĭca, ōrum, n., = τὰ χρονικά, Plin. 35, 9, 35, § 58; Gell. 17, 4, 5; 17, 15, 1; and in sing.: in primo chronico, id. 17, 21, 3: morbi, chronic, lingering, Isid. Orig. 4, 7; opp. acuti morbi.
Hence the work of Caelius Aurelianus is entitled De morbis acutis et chronicis.