Lewis & Short

Thăles, is and lētis (gen. Thaletis, Mel. 1, 17; Juv 13, 184; dat. Thaleti, Val. Max. 4, 1, ext. 7), m., = Θαλῆς, a celebrated Greek philosopher of Miletus, one of the seven wise men, and founder of the Ionic sect, Varr. R. R. 2, 1, 3; Cic. N. D. 1, 10, 25; 1, 33, 91; id. Ac. 2, 37, 118; id. Leg. 2, 11, 26; Sen. Q. N. 3, 13, 1; Min. Fel. 19, 4; Aug. Civ Dei, 18, 25.
Gen. Thalis, Prob. Cath. 1466 P.: Thaletis, Mel. 1, 17, 1; Sen. Q. N. 3, 14, 1; Juv. 13, 184.
Dat. Thali, App. Flor. 4, n. 18: Thaleti, Sen. Q. N. 4, 2, 22; Val. Max. 4, 1, ext. 7; Arn. 2, n. 9; Aug. Civ. Dei, 18, 25; 18, 37.
Acc. Thalem, Plaut. Capt. 2, 2, 24; Cic. Div. 1, 49, 111; App. Flor. 4, n. 18; Lact. 3, 14, 5: Thalen, Cic. de Or. 3, 34, 137; id. Div. 2, 27, 58: Thaleta, Serv. Verg. G. 4, 363; 4, 382: Thaletem, Cic. Rep. 1, 16, 25; Serv. Verg. A. 3, 241.
Abl. Thale, Cic. N. D. 1, 33, 91.
Hence, Thălētĭcus, a, um, adj., of or belonging to Thales: dogmata, Sid. Carm. 15, 89.