Is it ensure, insure, or assure?
1530s, "to digest," from Latin concoctus, past participle of concoquere "to digest; to boil together, prepare; to consider well," from com- "together" (see com-) + coquere "to cook" (see cook (n.)). Meaning "to prepare an edible thing" is from 1670s. First expanded metaphorically beyond cooking 1792. Related: Concocted; concocting.