Is it ensure, insure, or assure?
c.1300, "clerk, secretary," from Old French notarie "scribe, clerk, secretary" (12c.) and directly from Latin notarius "shorthand writer, clerk, secretary," from notare, "to note," from nota "shorthand character, letter, note" (see note (v.)). Meaning "person authorized to attest contracts, etc." is from mid-14c.; especially in notary public (late 15c.), which has the French order of subject-adjective. Related: Notarial.