@PleegWat no, that's the other way round. The meter has been redefined from the wavelength of something, I think. The physical artefact was initially supposed to be roughly equal to a fraction of the earth meridian, but there are some funny (for some geeky definition of fun...) stories about how it came to be.
And the kilogram is still the only unit being defined by a physical artefact, although I think this is in the process of being changed for some gravity related thing (some kind of torsion balance), or maybe a number of atoms, yes (although I'm not sure about the experimental setup that would make this a usable definition?). I'm sure someone will me to death with the details.
Historically, I think there were initially attempts to define it as the mass of a cubic decimeter (1 L) of water, but that was too dependant on the conditions (water purity, temperature etc.), so they used an artefact that was intended to be simply a physical embodiment of the abstract definition as the reference. There are also funny (yeah, in the same way) stories about a time towards the end of the 19th century when they wanted to make copies of it, and ended up changing which one was used as the actual reference, if I remember correctly.