estonteco

This is a word you can take apart in public: est- to be, -ont- the future active participle, -ec- the abstract quality. Literally, the state of being about to be. The same machinery gives pasinteco for the past and estanteco for the present, so learning one hands you three. Note that the participle on its own is an ordinary adjective: estonta jaro is a coming year, though for "next year" most speakers say venonta jaro. And in grammar talk, the -os tense is the futuro, a different word entirely.