This is the 11383rd most frequent Spanish word.
estonio
"Estonio" means "Estonian" in English, referring to something or someone from Estonia or the Estonian language.
In this sentence, 'estonio' is used as a noun to denote the nationality of the friend, indicating that he is from Estonia (male).
Mi amigo es estonio y vive en Tallin.
My friend is Estonian and lives in Tallinn.
Here, 'estonio' functions as a noun referring to the Estonian language, specifying the language spoken fluently.
Ella habla estonio con mucha fluidez.
She speaks Estonian fluently.
This usage has 'estonio' as an adjective (modified as 'estonia' to match gender with 'comida'), describing the type of cuisine served in the restaurant as being from Estonia.