Is it ensure, insure, or assure?
a junky old car
That beater gets her back and forth to work.
mid-14c., "an implement for beating;" mid-15c., "a person who punishes" (c.1200 as a surname); agent noun from beat (v.). Of various mechanical devices that "beat" in some sense from early 17c. Meaning "one who rouses game" is from 1825. Slang meaning "old car" is from c.1980.