os vs porta

os and porta both are nouns.

Word	Noun	Adjective	Verb	Adverb
os	Yes	No	No	No
porta	Yes	No	No	No

As nouns, porta is a hypernym of os; that is, porta is a word with a broader meaning than os:

Other hypernyms of os include opening, orifice.

os (noun)	porta (noun)
rigid connective tissue that makes up the skeleton of vertebrates	an aperture or hole that opens into a bodily cavity
a mouth or mouthlike opening