Lewis & Short

clancŭlum, adv. and prep. dim. [id.], secretly, privately (ante-class. but freq.).

        1. (α) Adv.: aucupemus ex insidiis clanculum, Plaut. As. 5, 2, 31: abire a legione, id. Am. 1, 3, 25: noctu advenire, id. Bacch. 2, 3, 83; 3, 1, 8; id. Cas. 2, 8, 8: congerere aliquod, Ter. Eun. 2, 3, 18: mordere, id. ib. 3, 1, 21; 3, 5, 41; 3, 5, 54: agere inter se, id. Heaut. 3, 1, 63; id. Phorm. 5, 6, 33.
        2. * (β) Prep. with acc.: clanculum Patres, Ter. Ad. 1, 1, 27; cf. clam.