reverie

If you’re relaxing on the beach, dreaming of how you will never have to get up and go back to work, you’re engaged in a reverie, or pleasant daydream.

There’s nothing wrong with reverie, but if you follow its path into English, you’ll see how closely it is connected to madness. The noun is from French rêverie, from a Middle French word meaning “wild speech, delirium,” from rever “to roam, speak wildly.” Middle French rever is also the source of English rave, as in raving mad.