J Meaning of J in English 1. n. (also j) (pl. Js or J's) 1. the tenth letter of the alphabet. 2 (as a Roman numeral) i in a final position (ij; vj). 2. abbr. (also J.) 1. joule(s). 2 Judge. 3 Justice. Oxford English vocab. Оксфордский английский словарь. 2012