Is it ensure, insure, or assure?
1640s, "person or thing that generates," from Latin generator "a begetter, producer," agent noun from past participle stem of generare (see generation). Meaning "machine that generates power" first recorded 1794; in sense of "machine that generates electric energy," 1879. Fem. generatrix attested from 1650s.
generator gen·er·a·tor (jěn'ə-rā'tər)
One that generates, especially a machine that converts mechanical energy into electrical energy.