Misc: a moist fertile spot in a desert is called a(n)?

Questions

(It.) - Slow and solemn.?

- A type of plainsong associated with Pope Gregory I (590- 604) existing as a large collection of ancient monophonic melodies which were until quite recently used in the Roman Catholic Church.?

(It.) - A bass line or pattern repeated over and over while upper parts proceed. The ground bass is a foundation for varied melodic, contrapuntal or harmonic treatment. Forms which use this device include the chaconne and passacaglia.?

(Ger.) - Markedly .?

(Lat. gemellus, 'twin') - A type of two-part late medieval English vocal music, with great use of thirds and sixths.?