thin person vs somebody

thin person and somebody both are nouns.

Word	Noun	Adjective	Verb	Adverb
thin person	Yes	No	No	No
somebody	Yes	No	No	No

As nouns, somebody is a hypernym of thin person; that is, somebody is a word with a broader meaning than thin person:

thin person: a person who is unusually thin and scrawny
somebody: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of thin person include individual, mortal, person, someone, soul.

thin person (noun)	somebody (noun)
a person who is unusually thin and scrawny	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential