The English spa term derives from the name of the famous health resort Spa in Belgium. This town rich of mineral springs was founded in the 14th century and sources trace back the naming of Spa to the Germanic word for spouting. During 18th and 19th century Spa got a lot of prosporous visitors and became a synonym for mineral springs and medicinal bath. That time also many British tourists visited Spa to have healing bath treatments and so the word found entrance into the English-speaking area. End of the 20th century the meaning of spa extended to wellness centers near a source of mineral water and to health areas of hotel resorts.
There is also an – often heard – argument that the word spa is actually an acronym based on the Latin phrase “sanitas per aquas” (“health through waters”) but there are no reliable sources to verify this. In fact the word spa was never used in the Latin culture and in the new-latin languages it is called “termae” (“terme” in Italian), therefore the acronym very likely is a later adaptation.