Comment by mcswell

This semantic variability in the relation between the two nouns of a compound is pretty common in compound nouns: "Y made of X", like "tomato paste", "Y used (somehow) for X" (like "toothpaste", "paintbrush", "electrical outlet"--here an adjective, but still a lexicalized phrase), "Y in X" ("treehouse"), "Y for X" ("doghouse"), "Y containing X" ("paint can"), not to mention metaphorical uses, with some etymological relation between X and Y ("moon shot", "crapshoot", "greenhouse"), and so on. Not to mention multi-word compounds, like "greenhouse gas"--but I'm sure you've seen lots of those in Germany :).