Think of a label that English sticks onto a country name: Argentina plus -ian, meaning belonging to that place. Once the label exists it can go on almost anything from there — a dish, a song, a team, a book, a piece of history — and it can also go on a person, and then it stands alone as the name for them. One word, one idea, two jobs in the sentence.
The supplied source gives Argentin(a) plus -ian, and traces the country name's element back through Latin argentum, silver. That explains the shape of the word; it is not an account of how the country was named.
所附資料給的是 Argentin(a) 加 -ian，並把國名裡的成分一路接回拉丁文 argentum（銀）。這說明的是字怎麼組成，不是在解釋國名的由來。
Wiktionary entries supplied in this packet: etymology_text on 'Argentinian' noun and adj (source_refs kaikki:3f6f69a190036ae4:265778106 and :265784562)
One branch
屬於阿根廷的：東西，還有人
兩個意思其實是同一張標籤。差別只在它貼在東西上，還是貼在人身上；貼在人身上時，它就自己當名詞用。
adjective · B1
Belonging to Argentina, or connected with Argentina and the people who live there. You use it for things from that country, such as its food, music, teams, cities, writers and history.
阿根廷的