Is it ensure, insure, or assure?
1530s, from Middle French conférer (14c.) "to give, converse, compare," from Latin conferre "to bring together," figuratively "to compare; consult, deliberate, talk over," from com- "together" (see com-) + ferre "to bear" (see infer). Sense of "taking counsel" led to conference. The meaning "compare" (common 1530-1650) is largely obsolete, but the abbreviation cf. still is used in this sense. Related: Conferred; conferring.