The word helicopter doesn’t come from heli- and -copter; it was actually formed from helico- and -pter. That hasn’t stopped us making new words from the wrong history.
Etymology is the history of words. It’s a funny discipline, though; people have been talking word histories for a long time, but they very often get them wrong. Folk etymologies are fake histories of words – ones that sound convincing but aren’t actually supported by historical evidence. Take hamburger for example: it actually means something that comes from the German city of Hamburg. The (incorrect) etymology of ham+burger sounds right, though. So right that we now use -burger as a suffix (cheeseburger, fishburger, etc.).
This process is called rebracketing. It looks something like this:
- A word is formed by connecting two or more words / suffixes / etc.
- The word is divided a different way according to some folk etymology. It seems to make sense to divide it up that way, in other words.
- The new division becomes a part of related words, and collects a meaning not previously attached to it.
So: hamburg+er, hamburger, ham+burger, cheese+burger.
It turns out that there are a lot of examples of this happening. The one that I first heard about (from a Tweet, linked below) is the word helicopter. It actually comes from the Greek heliko- (“turning”) and -pteron (“wing”), but we now use copter on its own and heli- in words like helipad and heliport.
Helico+pter, helicopter, heli+copter, heli+pad.
Some more examples:
Cybern+etics, cybernetics, cyber+netics, cyber+space.
Labrad+oodle, labradoodle, labra+doodle, goldendoodle.
And here’s one more, a little closer to home:
Web+log, weblog, we+blog, blog!
[Thanks to @clapifyoulikeme for drawing my attention to this topic.]