céans, here within. The word was already antiquated

6. magnifique. In the etymological sense of “ do things on a large scale.”

7. un dessus, etc. A soprajio (or ténor), \counter-tenor (or alto).

8. basse de viole. A string instrument, something like the ’cello, which has supplanted it.

9. théorbe, theorbo. An old instrument of the lute family, having two heads.

10. clavecin, harpsichord, the predecessor of the piano-forte.

11. basses continues. The instruments mentioned would play a continuons suite of chords {basses continues), while the voices were singing. Such chords were the only ones written out on the score (“figured bass ”). The violins played only the préludés and the ritorn elles. See line 25.