junior vs Junior

junior and Junior both are nouns.

Word	Noun	Adjective	Verb	Adverb
junior	Yes	Yes	No	No
Junior	Yes	Yes	No	No

junior (noun)	Junior (noun)
the younger of two persons	a son who has the same first name as his father
a third-year undergraduate
term of address for a disrespectful and annoying male

junior (adjective)	Junior (adjective)
younger; lower in rank; shorter in length of tenure or service	used of the younger of two persons of the same name especially used to distinguish a son from his father
used of the third or next to final year in United States high school or college
including or intended for youthful persons