Form of Esperanto (3)

I believe the answer is:

ido

(Other definitions for ido that I've seen before include "a language? That's unnatural" , "Required affirmative in wedding ceremony" , "International language" , "Wedding vow" , "Obscure language" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.