In french there's also the curious case of "pesanteur" (gravity), which is feminine; so "la pesanteur" (the gravity). But the absence of gravity is "apesanteur" (weightlessness), which is also a feminine word; so "l'apesenteur". So we have two slightly different words that actually sound exactly the same with their articles. It's only a few years ago that people decided to change the prefix and use "impesanteur" inst…
They are two different words though. The prefix "a" means "without" in many other words too.
Never heard "impesanteur" but I have few friends who are cosmonauts obviously :)