useless trivia: What Word Means: A Rebeck - A Moorish Three-stringed Fiddle?

Questions

City-state and the largest port in Germany?

A method of voice production by male singers used to vocalise notes higher than their normal range?

Essential framework of any structure, outline consisting of bare essentials?

Designate as officially secret, and not for general disclosure?

German songs, particularly of the romantic period, usually for solo voices?