Inflected forms: pl. j's or J's also js or Js 1. The tenth letter of the modern English alphabet. 2. Any of the speech sounds represented by the letter j.3. The tenth in a series. 4. Something shaped like the letter J. 5.J The hypothetical traditional source of those portions of the Pentateuch in which God is referred to with the Tetragrammaton rather than as Elohim.