Is it ensure, insure, or assure?
1520s, borrowing of Latin jota, variant spelling of Greek iota "the letter -i-," the smallest letter in the alphabet, hence the least part of anything.
"to make a short note of," 1721, from jot (n.). Related: Jotted; jotting.
or Iota, the smallest letter of the Greek alphabet, used metaphorically or proverbially for the smallest thing (Matt. 5:18); or it may be = yod, which is the smallest of the Hebrew letters.