Is it ensure, insure, or assure?
early 15c., "having great power or force," from Latin praevalentem (nominative praevalens) "of superior strength; mighty," present participle of praevalere "to be more able" (see prevail). Meaning "extensively existing, in general use" is from 1650s.
1590s, "fact of having mastery," from Middle French prévalence (15c.), from Late Latin praevalentia, from praevalens, present participle of praevalere (see prevalent). Meaning "condition of being widespread or general" is from 1713.
prevalence prev·a·lence (prěv'ə-ləns)
The total number of cases of a disease in a given population at a specific time.