All 4 Uses

prelude
in
The Magic Mountain
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This was a prelude to his cigar, a Maria Mancini, a very tasty brand from Bremen—we shall come to speak about that again—whose spicy toxins blended so satisfyingly with those of his coffee.†
Chpt 2.2 *
The first step toward evil, toward lust and death, was doubtless taken when, as the result of a tickle by some unknown incursion, spirit increased in density for the first time, creating a pathologically rank growth of tissue that formed, half in pleasure, half in defense, as the prelude to matter, the transition from the immaterial to the material.†
Chpt 5.7
A violin, in solo, offered a fanciful prelude.†
Chpt 7.7
Purely instrumental, with no vocals, it was a symphonic prelude of French provenance, scored for a small ensemble, at least by modern standards, yet fitted out with all the tricks of modern tone coloring and cleverly calculated to set the soul spinning a web of dreams.†
Chpt 7.7

Definitions:

(1) (prelude)
something that comes before and prepares for what follows; in music, a short piece that introduces a larger work or stands alone as a brief, expressive piece (often for piano)

In everyday use, a prelude is an event or action that leads up to something more important, like a small disagreement being a prelude to a larger conflict. In music, the word can mean a short opening piece (for example, before an opera scene) or a short, self-contained work, often written for piano or organ, that sets a mood.
(2) (meaning too rare to warrant focus)