vat (n.) Look up vat at
c. 1200, large tub or cistern, "especially one for holding liquors in an immature state" [Century Dictionary], southern variant (see V) of Old English fæt "container, vat," from Proto-Germanic *fatan (source also of Old Saxon, Old Norse fat, Old Frisian fet, Middle Dutch, Dutch vat, Old High German faz, German faß), from PIE root *ped- (2) "container" (source also of Lithuanian puodas "pot").