Nevermore means ‘never again’ — from this time on, not one more time. It is an old, literary word. You will almost never hear it in the street or in ordinary classroom talk. English speakers know it best from a famous poem, The Raven, where a bird keeps saying ‘Nevermore’. If you use it in normal talk, people may smile, as if you are quoting a book on purpose. Though actually, the pieces are ordinary: it is simply never + more, going back to Old English nǣfre mā. The whole word feels grand; the parts do not.