Zimmermann
Zimmermann is a German occupational surname which is literally an older German term for a carpenter. The modern German terms for the occupation of carpenter are Zimmerer, Tischler, or Schreiner, but Zimmermann is still used.
Zimmer in German means room or archaically a chamber within a structure. The German man or mann is, in English the extra n is ignored, man or worker. Combining the two German words you get a worker of wood or literally translated room man or room worker.
Zimmermann, as a surname is often confused with Zimmerman. The loss or addition of the double "n" may imply many things. This may include linguistic, racial, ethnic, religious or other cultural variations.
Many German names were often Anglicized or simplified by immigration officials upon entry into the United States. With Zimmermann the double 'n' Zimmermann was often seen as redundant in countries where English was spoken. As a part of routine, German names were often Anglicized or simplified later by immigrants to better fit in. Zimmerman became Carpenter for example. Sometimes this was done by immigration officials upon entry into the United States when the immigrant did not know how to spell their name and that variant became the legal name.