SICA, dim. SICILA, whence the English sickle, and SICILICULA (Plaut. Rud. iv.4.125), a curved dagger, adapted by its form to be concealed under the clothes, and therefore carried by robbers and murderers [Acinaces] (Cic. Cat. iii.3). Sica may be translated a scimitar to distinguish it from Pugio, which denoted a dagger of the common kind. Sicarius, though properly meaning one who murdered with the sica, was applied to murderers in general (Quintil. x.1 § 12). Hence the forms de sicariis and inter sicarios were used in the criminal courts in reference to murder. Thus judicium inter sicarios, "a trial for murder" (Cic. pro Rosc. 5); defendere inter sicarios, "to defend against a charge of murder" (Phil. ii.4).

William Smith, A Dictionary of Greek and Roman Antiquities (London: John Murray, 1875), 1044.