The Fosi were a Germanic tribe. Tacitus, in his Germania mentions them as being neighbours of the Cherusci, and they suffered alongside the Cherusci in their downfall.^[1] He also noted that before their mutual downfall, the Fosi were less prosperous than the Cherusci.^[2] The two tribes, however, had been dependents in their prosperity, so they shared that same adversity on equal terms during their decline.^[1] The etymological origin of the name Fosi is not known with certainty. The name may derive from the proto-Germanic *fuhsaz, signifying "fox".