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Old English trog, from Proto-Germanic *trugoz (cf. Old Frisian, Old Saxon, Old Norse trog, Middle Dutch troch, Dutch trog, Old High German troc, German trog), perhaps ultimately from PIE *drukos, from root *dru- "wood, tree" (see tree). Originally pronounced in English with a hard -gh- (as in Scottish loch); pronunciation shifted to -f-, but spelling remained.
Diarrhea; the SHITS (1904+)