Is it ensure, insure, or assure?
1590s, "one who performs mechanical or surgical operations," agent noun from operate (v.) or from Late Latin operator. Meaning "one who carries on business shrewdly" is from 1828. Specific sense of "one who works a telephone switchboard" (1884) grew out of earlier meaning "one who works a telegraph" (1847).
operator op·er·a·tor (ŏp'ə-rā'tər)
An operator gene.
in mathematics, any symbol that indicates an operation to be performed. Examples are x (which indicates the square root is to be taken) and ddx (which indicates differentiation with respect to x is to be performed). An operator may be regarded as a function, transformation, or map, in the sense that it associates or "maps" elements from one set to elements from another set. See also automorphism.