Is it ensure, insure, or assure?
past participle adjective from designate. Designated hitter introduced in American League baseball in 1973, soon giving wide figurative extension to designated, e.g. designated driver, by 1985.
1640s, from Latin designatus, past participle of designare (see design (v.)).
As a verb, from 1791, from designate (adj.) or else a back-formation from designation. Related: Designated; designating.