It's the name of our sun. Sun is what it is (or star). Sol is its name.
The argument is rather pedantic to me since the word Sun comes from the old English, Germanic, and European, whereas Sol comes from the Latin, Helios from the Greek, svár Sanskrit, etc. They are all valid names for our local star.
"The Boss said please take the day off"
"Our Boss is nice"
"Jill is the boss"
"The Sun is bigger than any planet in our solar system"
"Our Sun is 8 light minutes away"
"Sol is the name of our sun"
I've not once heard a solar physicist use "sun" as a name
"Sun is bright" - bad grammar