WordNet sense 1 (a son who has the same first name as his father):

Jnr, Jr

WordNet sense 2 (of the younger of two boys with the same family name):

minor

WordNet sense 3 (inferior in rank or status):

inferior, secondary

WordNet sense 4 ((used of living things especially persons) in an early period of life or development or growth):

immature

WordNet sense 5 (used of the third or next to final year in United States high school or college):

next-to-last, third-year

WordNet sense 6 (lying between two extremes in time or space or degree):

intermediate, intermediate