(3 syl.). A legendary hero of Germany, who wins the affections of Lisaura; but Lisaura, hearing that Sir Tannhäuser has set out for Venusberg to kiss the queen of love and beauty, destroys herself. After living some time in the cave-palace, Sir Tannhäuser obtains leave to visit the upper world, and goes to Pope Urban for absolution. “No,” said his holiness, “you can no more hope for mercy than this dry staff can be expected to bud again.” On this the knight returned to Venusberg. In a few days the papal staff actually did bud, and Urban sent for Sir Tannhauser, but the knight was nowhere to be found.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Tannhauser from Fact Monster: