An Etymological Dictionary of Astronomy and Astrophysics

1. Of more recent appointment or admission, as to an office or status; of lower rank or standing.
   

2. (in American universities, colleges, and schools) noting or pertaining to the class or year next below that of the senior
   

3. Younger, designating the younger of two men bearing the same full name, as a son named after his father; often written as Jr. or jr. following the name (Dictionary.com).

Etymology (EN): From L. iunior, comparative of iuvenis “young, young man,” cognate with Pers. javân, → young.

Etymology (PE): Kehtar, comparative of keh “small, little,” → decrease.