This is the 38th most frequent Lithuanian word.
vienas
"Vienas" means "one" in English.
In this context, 'vienas' is used as an indefinite pronoun meaning 'one' as in 'one of'.
Vienas iš draugų man parašė.
One of my friends wrote to me.
Here, 'vienas' is used as a numeral indicating the quantity 'one'.
Aš turiu vieną knygą.
I have one book.
In this sentence, 'vienas' is used as an adjective meaning 'alone'.