From callidus +‎ -ulus.

• (Classical Latin) IPA^(key): [kalˈlɪ.dʊ.ɫʊs]
• (modern Italianate Ecclesiastical) IPA^(key): [kalˈliː.du.lus]

callidulus (feminine callidula, neuter callidulum); first/second-declension adjective

1. diminutive of callidus (“cunning, sly”)
   • c. 303 CE, Arnobius, Against the Pagans 2.68:

     et hunc similiter morem, non fraude callidula, et nominum ambiguitate mutastis?

     have you not, in like manner, changed this custom too, by means of cunning deceit and ambiguous names?

First/second-declension adjective.

• “callidulus”, in Charlton T. Lewis and Charles Short (1879), A Latin Dictionary, Oxford: Clarendon Press
• “callidulus”, in Gaffiot, Félix (1934), Dictionnaire illustré latin-français, Hachette.