The English word “flamboyant” is taken directly from French. That is, in French the word is the same, but the meaning differs. And the meaning in French has changed in interesting ways since the 1500s, and also since the 1800s, which is when it started to appear in English.
The French word is probably older than the 1500s, but I don’t have any French reference books to consult. “Flamboyant” originally meant “on fire” or “flaming.” This is not quite the same as “burning;” with “flamboyant” the point is the flames themselves. In France in the middle ages, they were busily building fancy cathedrals. The architectural style was broadly called “gothic,” but there are more precise types of “gothic” architecture too. In the 15th century one of those types began to appear; it added decorative curved carvings, taller arches, and higher, narrow windows pointed at the top. These details were all intended to resemble flames. So the architectural style was, sensibly enough, called “flamboyant.”
The flamboyant style was a great deal more ornate than what had come before, and some of the more conservative observers looking back a couple of centuries later thought this fancy new stuff had gone too far and was much too florid. That sort of reaction was enough to propel “flamboyant” into general usage with the figurative meaning of just about anything or anyone that was overly showy.
That was where “flamboyant” was, semantically, when it made the trip over the English Channel. When it arrived in England it didn’t bring with it any semblance of the original “in flames” meaning. And it kept its association with Medieval gothic architecture only among the crowd having an interest in such things (from an 1832 article in “Archaeologia”: “They are of all dates, from Early French to the latest Flamboyant”). What it primarily brought with it to English was the figurative “over the top” sense. English speakers wasted little time in using it that way: “That flamboyant penmanship admired by our ancestors.” (1879, by E. Dowden in “Southey”); “Sir Francis Burdett indulged in flamboyant perorations.” (1883, by L. Wingfield in “Abigel Rowe”).
Another common usage of “flamboyant” also emphasized things that were as bright and colorful as flames, along with usually being showy and gaudy: “…daughters, in flamboyant ribbons, were among the belles of the parish” (1867, by D.G. Mitchell in “Rural Studies”).
In modern usage “flamboyant” is often used to describe fashion and styles of apparel. It’s applied to extravagant costuming used by Cher, for example, or female impersonators such as RuPaul or Dame Edna. A comic line used in more than one movie runs like this: “is he gay?” “Flaming.” The “flaming” in that context is a sort of back formation from, you guessed it, “flamboyant.”
