The words adolescence, adolescents sound the same but have different meanings and spellings. Why do adolescence, adolescents sound the same even though they are completely different words?
The answer is simple: adolescence, adolescents are homophones of the English language.
The period of physical and psychological development from the onset of puberty to maturity.
A transitional period of development between youth and maturity: the adolescence of a nation.
Plural form of adolescent.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.