Is it ensure, insure, or assure?
1610s, confident, "(male) person trusted with private affairs," from French confident (16c.), from Italian confidente "a trusty friend," literally "confident, trusty," from Latin confidentem (nominative confidens), present participle of confidere "to trust, confide" (see confidence). The spelling with -a- came to predominate 18c. and might reflect the French pronunciation.