Proposal: Uranus et. al. should no longer be called "plane-ettes".

[Ionathus]

That's what I grew up being taught, but it's not what they are now!

Jupiter and Saturn as 'Gas Giants', Uranus and Neptune are now 'Ice Giants' whatever that means.

Ice Giants, you say??

Okay, so if my example is bad let's ignore it and get at the actual point: Why is the fact that "planet" is spelled similar to "plane" of any significance?

We're getting into false cognates here, which is one of my favorite quirks of language. The answer, as others have pointed out, is simply that "language is like that sometimes." Especially for a language that draws from multiple other languages, and especially especially for English, the most thoroughly-mixed bastard child of the Romantic and Germanic languages' offspring[citation needed]. English wound up with a lot of duplicate words with at least one Latin root and one Germanic root, and they don't always have the same Proto-Indo-European origins.