There are four or five competing theories for the origin of the word “beer” and, frankly, none of them is particularly convincing.
The same is true of the word “ale”, as it happens: despite “ale” and its sisters, such as öl in Swedish and alus in Lithuanian, being found in languages from Britain to the Black Sea via the Baltic, no linguist has any good idea how it originated, with some of the ideas put forward being way out there in the unlikeliness ionosphere.
Of the four “great” families of words meaning “alcoholic drink made from malted grain”, however, we can be reasonably certain about the origins of the other two, the Slavonic “pivo” group and what might be called the “cerevisia” group, after the Latin word for “beer”. (Or, to be accurate, one of the Latin words for beer, since as well as the spelling we’re familiar with in the name of brewing yeast, Saccharomyces cerevisiae, the word also occurs in various Latin documents in the forms cervisia, cervesia, cervese, cervesa and cervisa.)
Taking this “cerevisia” group first, the Romans, who were wine drinkers rather than beer brewers, nicked their word for beer, in all its spellings, from speakers of a Celtic language. The original Proto-Celtic for “beer” was probably something like *kormi (that asterisk is the etymologist’s symbol indicating a word that has not been attested, but whose form can be worked out on the basis of later variants), going back to an earlier Proto-Indo-European word *kerm- (that dash means there was an ending on *kerm but we don’t know what that ending was.) *Kerm looks to be the root of a few other words in the Indo-European family, such as Russian korm, meaning “fodder,” an old Slavonic word krma, meaning “nourishment” or “food”, and Latin cremor, meaning “broth”, or “pap”.
In Gaulish, the Celtic language spoken in what is now France, the original *kormi had become curmi, so the Romans must have borrowed the word for “beer” from a bunch of Celts (perhaps the “Cisalpine” ones, living on the Italian side of the Alps) whose accent had turned that “curmi” into “*cermi”. What about the “m” becoming “v”? A general change shift in the “m” sound to “v” in the middle of words appears to be something that was happening, in British Celtic, at least, during or soon after the Roman occupation of this island, so that, for example, the British kingdoms of Dumnonia and Demetia became, respectively, Devon and Dyfed (pronounced “duvv-ed”). It looks like this m-to-v change was taking place in Continental Celtic earlier than that, perhaps some time between the Greek writer Posidonius, who lived from around 135BC to 50BC, and the Roman writer Gaius Plinius, better known today as Pliny, who lived from AD23 to 79. Posidonius said the Celts of Southern Gaul drank a wheat-and-honey beer called corma, still with the “m”, while a century or so later Pliny gave the name of Gaulish beer in his Historia Naturalis (Natural History) as cervesia, now with the “v”, and with an added “s” as well.
It is from the form cervisa that French derived the word cervoise, still the term used in French for unhopped ale (and the origin of the French surname Leservoisier), while the Spanish and Portuguese look to have turned the cervesa version in Latin into cerveza and cerveja respectively. (In Galician, spoken in northern Spain, the word is cervexa, and it is still cervesa in Catalan.) The Spanish exported the word to the lands they conquered, so that, for example, in Tagalog (a language spoken in the Philippines, once part of the Spanish empire) the word for beer is serbesa.
In Britain, as on the continent, that change from m to v meant that the old Brythonic (British Celtic) word for “beer”, *korm, altered its form, becoming *cwrf (pronounced “coorv”) in old Welsh, then cwrwf, before losing the f to become modern Welsh cwrw, pronounced “cooroo”. (Welsh being what is known technically as a “mutating” language, incidentally, certain initial consonants change when nouns are used with prepositions, and that includes hard “c”, which becomes hard “g”: I am grateful to a young woman called Kat for imparting the information that the essential order at the bar in grammatically correct Welsh would be “Dau peint o gwrw ac baced crisps, plis.” This is particularly important in the Lleyn peninsula, where you wouldn’t want the locals to think you were from Swansea.
Unlike Welsh, the sister Celtic languages Cornish and Breton kept the f/v after the change from “m”, so that “beer” in Cornish is coref, and in Breton coreff. In the more distantly related Celtic language Irish, however, the word for beer stayed closer to the Proto-Celtic original, being coirm. By the time the Irish began settling in what was to become Scotland, though, about AD 500 or so, it looks as if the word coirm had dropped into disuse, since the modern Irish and Scots Gaelic for “beer” is lionn, which originally just meant “drink”. Coirm seems to have stayed on in Irish as a word meaning “feast”, however, just as an “ale” in early modern English also meant a feast, as well as a drink.
(Incidentally, if you find anyone trying to assert that the word cerevisia comes from Ceres, the Roman goddess of agriculture, please give them a slap: this is perhaps the oldest beer myth in the world, going back at least as far as St Isidore of Seville (circa 560 – 636), who wrote a book 14 centuries ago called Etymologiae which followed the usual Roman habit of treating all foreign languages as bastard forms of Latin, and trying to find Latin roots for every foreign word.)
If you can order beer from Madrid to Manila with words derived originally from the Celtic, you can also go far with the Slavic pivo. It originally just meant “beverage” in Old Common Slavonic, which itself inherited the word from the Proto-Indo-European base *po-/*pi- “drink”: piti was the Old Slavonic for “to drink”. Other words from the same root include “potion”, “potable”, the Greek pinein, “to drink”, and, indeed, “beverage”, via Latin bibere, “to drink” (which we shall be coming back to). Today pivo or something almost identical is the easily recognised word for “beer” across most of Eastern Europe and (thanks to the former Russian/Soviet empire) far into Central Asia: pivo itself in Slovene, Croatian, Serbian, Bosnian, Czech, Slovak, Macedonian, Ukrainian, Russian, Azerbaijani, Kyrgyz and Uzbek; piwo in Polish and Turkmen; and piva in Belorussian and Uighur.
In the middle of pivoland sits the curious case of Hungarian, a non-Indo-European language, unlike its neighbours, where the word for “beer” is sör. An archaic and dialectical variant of sör, sometimes used informally, apparently, is ser. You might be tempted to guess that this comes from the cerevisia family. Don’t be. Guessing by untrained amateurs (in which category I definitely fall) will get real etymologists laughing and sneering, and pouring soot and eggs on your head.
As it happens, although there probably were Celtic tribes living in and/or near ancient Pannonia, the name for Hungary before the Magyars moved there (the Boii, for example, who gave their name to Bohemia), we can be pretty certain the local word for beer in Roman times was camum. A delegation from the Eastern Roman Empire to the court of Atilla in Pannonia in AD 448 found the locals handing out “a drink of barley … called camum”, and camum was one of three types of beer (the other two being the Celtic cervesia and the Egyptian zythum) mentioned in the Roman Emperor Diocletian’s lengthy Edictum de Pretii, Edict on Prices, in AD 301, an unsuccessful attempt to curb inflation by setting maximum prices on everything from a haircut to a pound of sausages.
In fact the best source for sör appears to be a word for “beer” in Turkic languages, sıra (that’s an “i” without a dot there: sıra is pronounced approximately as “sera” in the French expression Doris Day song Que sera, sera. The ancestors of the modern Hungarians lived alongside Turkic-speaking peoples for around 400 years, up until they moved to the Danube lands shortly before AD 900 or so, and picked up quite a few words from them (including the word for “word”, apparently). At least two Turkic languages, Kazakh and Tatar, still use sıra for “beer”, though most others seem to have substituted versions of pivo, and Turkish uses bira, derived, obviously, from “beer” itself.
And what of the origins of the word “beer”, and of “ale”? More shortly …