Definition of: junior

(jn′yər) adjective
1. Younger in years or lower in rank.
2. Denoting the younger of two: opposed to senior and distinguishing a father from a son, usually abbreviated Jr.
3. Belonging to youth or earlier life.
4. Later in point of existence or occurrence: junior securities.
5. Pertaining to the third year of a high–school or collegiate course of four years.
—noun
1. The younger of two; one later or lower in service or standing; a younger person.
2. A student in the third or junior year of a high–school, college, or university course. [<L junior, comp. of juvenis young]