Lewis & Short

clandestīnus, a, um, adj. [for clamdies-tinus; cf. matutinus; v. Corss. Ausspr. 1, p. 461 sq.], secret, hidden, concealed, clandestine (class. in prose and poetry): suspitio, Plaut. Am. 1, 2, 28: nuptiae, id. Cas. 5, 3, 6: natura, Lucr. 1, 779: motus materiaï, id. 2, 127: scelere, Cic. Sull. 11, 33; cf. Liv. 42, 18, 1: introitus, Cic. Off. 2, 23, 81; cf. Suet. Ner. 48: colloquia cum hostibus, Cic. Sen. 12, 40: consilia, Crassus ap. Cic. Or. 66, 223; Caes. B. G. 7, 1; cf. Liv. 42, 24, 3: nuntiis legationibusque, Caes. B. G. 7, 64: fuga, Auct. B. G. 8, 33: foedus, Liv. 3, 36, 9; Sil. 7, 267: denuntiatio, Liv. 4, 36, 3: coetus, Tac. A. 2, 40; 4, 27.
Adv.: clandestīnō, secretly; only Lucil. ap. Non. p. 38, 19, and Plaut. Mil. 4, 1, 10.