Extract from The Changing Face Of Warminster by Wilfred Middlebrook, published in 1971:
It must surely be a fact that more printers’ ink has been squandered on futile discussions concerning the origin of the name of Warminster than on any other place-name in the country.
The only certainties are the varied spellings since the first mention of Worgemynster in the Anglo-Saxon Charter around A.D. 900. In Domesday the Normans changed it to Guerminstre, then through the Plantagenet period, by an easy transition of Guer into Wer (as Guilou into Wily) we find ever-varying forms of the name ranging from Werminster in 1115, and Warmestre in 1496, to our present-day Warminster.
Many writers, including the historians Hoare and Wansey, have quickly disposed of the matter by presuming that a minster or monastery once stood on the banks of a river or stream called the Were. Daniell declares that “if any brook bears the name of Were, it seems to that which is now called the Biss, which rises in Upton Scudamore and runs through Trowbridge.”
Failing the “Minster on the Were” theory, there have been some fantastic flights of fancy in an effort to solve the puzzle. Working on the names Guerminstre and Worgemynster, one writer finally translated the result into “the place of waters where the blue sky-god was worshipped in a green place, and at which a Dragon protected the Spirit of a Chief in his Grave.”
More down to earth, Daniell suggests that Worgemyn or Guermin is the name of an ancient Wiltshire Chief, so that Warminster means “the headquarters of Worgemyn.”