cinio is used for both 'lunch' and 'dinner'.
The various terms that we use on this course for the names of meals are explained in the notes (https://forum.duolingo.com/comment/17638579) for the section 'Present 2' - https://www.duolingo.com/skill/cy/Present-2/tips-and-notes
To see how to find the course notes generally, go to https://forum.duolingo.com/topic/924/hot and read the discussion 'Course tips and notes'. The 'duome' link there is useful for browsing all the notes in one place. We recommend reading the notes for each new section as you start it.
when you click on the word it translates lunch and dinner too so weird they don't accept dinner. I reported it obviously. In a different exercise i put lunch and wanted to try using dinner but is not accepted ,so why it's given as a translation option ? just saying weird:-)