It paid a premium-inclusive £3400 (£2800 hammer price) for the tankard that was made in Bruton in the 18th century.
The lot was estimated at £2000-2500 and the museum was able to make the winning bid after it raised funds from local people as well as the Art Fund and the V&A Purchase Grant.
The tankard was made by local goldsmith Gabriel Felling. Felling is regarded as one of the most important provincial smiths of the late 17th and early 18th century. He trained in London as one of King Charles II's royal goldsmiths. He was a Protestant immigrant and is believed to have left London in 1676 or 1677 for Somerset.
He was first recorded working in Bruton in 1678 and may have come to the town because of the wealthy Berkeley family, who had acquired Bruton Abbey after the dissolution of the monasteries.
Museum chairman Douglas Learmond said: “The volunteer-run museum had long wanted to have a piece of Felling silver, but it was well aware that all his work commanded high prices.
“Felling silver rarely comes on the market so if it was to acquire the tankard the museum would have to move quickly. The acquisition of the tankard will help illustrate the wealth around Bruton in the 16th to 18th century period.”