Thanks for the error report, which has made my day. The word is actually correct!
From the Concise Oxford: 'senary adj. rare relating to or based on the number six'.
The Portuguese adjective senário (six-related) is a homophone of the noun cenário, meaning 'scenery' in the theatrical or cinematic sense, from cena 'stage'. I suspect you have been tripped up by this amusing little curiosity.
Yes, indeed! My partner (who is Portuguese) had written 'senary' in place of 'scenery' in a piece of writing and when she showed me the entry in the wordreference dictionary we thought it was a mistake - we later discovered we had the wrong spelling of the Portuguese word and that's where the confusion had arisen! Definitely helpful for my Portuguese, and her English! Many thanks for your kind reply