My explanation that Klawitter comes probably from the Latvian word "klava" which means "maple" is from a copy of a book on Germany familiy histories. As I only have a copy of the Klawitter pages I cannot tell more about the book. It's probably from the early "3rd Reich".
But Mary de Francesco found a different theory:
I wanted to say that I heard the klawitter s may be of Danish or even Lithuanian origins. There is no klawitter surname in those countries, but there exists some klawitter families that say the klawitter name id from denmark and it was germanized, they will tell me more later, and some genealogies say that it may have come from the Lithuanian surname Klevaitis, or "son of a famous man", not from Klava meaning acorn, because there is no son of the acorn.... this Klevaitis name would be from eastern orthodox lithuanian people though as it would have come from the greek name Kleopas, meaning son of a famous father.
The explanation that Klawitter comes from "klar" + "Wetter" (clear + weather) however is a funny but wrong myth.
In the 1850ies many people were illiterate, and many people leaving Europe lost their documents. So when it came to write their name for the first time, someone (the immigration officer) had to guess from their pronounciation.