The Collaborative International Dictionary of English v.0.48:
Jnr \Jnr.\ n. Abbreviation for Junior, used after a name by a son who has the same first and last name as his father; -- less commonly used than Jr. Syn: Junior, Jr. [WordNet 1.5]WordNet (r) 3.0 (2006):
jr. adj 1: used of the younger of two persons of the same name especially used to distinguish a son from his father; "John Junior"; "John Smith, Jr." [syn: younger, jr.]