Everyone translates the name as "under-sea", and it is probably wrong.
Fomoire is transparently a compound of fo, meaning under or beneath, and something else. The popular reading takes the second element as muir, sea, which produces sea-giants and fits the way they arrive — by ship, from the north and west, demanding tribute. The reading most linguists now prefer takes it from a different element related to a word for a phantom or terror, the same one that may lie behind the Morrígan's name. That gives something closer to "under-phantoms" or "nether-demons": beings from below rather than from offshore.
The distinction matters, because the maritime reading has quietly shaped how they are pictured for two centuries.
What they actually look like in the texts
Inconsistent, and this is the most interesting thing about them.
The Book of Invasions describes companies of them as having one arm and one leg, and later summaries turn that into a race of misshapen monsters. But their prince Elatha arrives in a silver vessel with golden hair down his back and is described in the language of an ideal nobleman. His son Bres is the standard against which every beautiful thing in Ireland is measured. Ethniu, Lugh's mother, is a Fomorian, which makes the greatest of the Tuatha Dé half of what he is fighting.
So the Fomorians produce the most beautiful man in Irish literature and the ugliest, and both are correct according to different passages. This is not a scribe being careless. It is what happens when an opposing supernatural group is defined by opposition rather than by species — the same pattern as the Norse giants, who are enemies of the gods and also their in-laws, and the Greek Titans, who are the previous generation rather than a different kind of being.
The sequence of oppressions
They are the constant in the invasion scheme. Every people who settles Ireland has to deal with them:
- Partholón's people fight them and win a battle before being wiped out by plague.
- Nemed's people are subjected to a heavy tribute — two-thirds of their children, their corn and their milk, delivered each Samhain — paid to Conand in his tower on Tory Island. They storm the tower and are then destroyed by a counter-attack and a sea-flood, with only a handful escaping.
- The Fir Bolg are largely left alone; the Fomorians in this stretch are background.
- The Tuatha Dé Danann submit to tribute under Bres, and then break it at the second battle of Mag Tuired.
The repetition is structural. The Fomorians are what stands between each settlement and secure possession of the island, and the pseudo-history needs them to be there every time, which is why they are never satisfactorily destroyed.
Three theories about who they represent
Each has had its period and each is worth knowing.
- Pre-Celtic natives. Nineteenth- and early twentieth-century scholarship read them as a memory of an earlier population subjugated and demonised by incomers. The theory is now largely abandoned: the texts consistently make them a supernatural group with divine genealogies, not a subject people, and the invasion scheme is a learned construction rather than a folk memory.
- Viking raiders. Sea-borne strangers who arrive from the north, take tribute, fortify islands and are impossible to be rid of describes the ninth and tenth centuries in Ireland with uncomfortable accuracy, and the invasion literature reached its surviving form in exactly that period. This is best stated as plausible colouring of an older idea rather than as its origin — the Fomorians appear in material that predates the Norse.
- Chaos powers. The comparative reading: an older, disorderly generation of supernatural beings, related to the gods by blood, whose defeat establishes the current order and whose defeat is never permanent. This fits the texts best and explains the intermarriage that the other two theories have to work around.
Balor, and the shape of the enemy
Their most famous member has his own dossier, and the traits usually attributed to Fomorians generally turn out to be his: the single destroying eye, the island fortress, the tyranny. It is worth noticing how much of the group's reputation rests on one figure, and how much of that figure's story comes from nineteenth-century folk collection rather than from the medieval texts.
Their other leaders are less lurid. Indech mac Dé Domnann is a king who fights a battle and dies in it. Elatha is a diplomat who tells his own son he deserved to lose his throne. Tethra owns a talking sword. Cichol Gricenchos, the earliest of them named, is a footless one.
Where the word went
"Fomorian" has had a modest but persistent modern career as a name for a class of monster. Dungeons & Dragons uses it for a race of deformed giants exiled to a fairy realm, which owes more to the one-armed one-legged descriptions than to anything else in the corpus, and fantasy fiction set in Ireland reaches for the word whenever it needs an antagonist that is not quite a demon. What almost never survives the translation is the family relationship — that the war is fought between cousins, and that the hero who ends it is the enemy king's grandson. That relationship is drawn on the Celtic family tree, and the reasons this material is shaped as it is are set out at the Celtic tradition hub.
Were they worshipped?
There is no evidence of it and no obvious reason to expect any. They exist as a narrative category inside a Christian pseudo-history, and unlike several of the Tuatha Dé — who leave traces in glossaries, place-names and, on the Continent, in inscriptions — the Fomorians have no cult residue at all. What they may preserve is a genuine older idea about hostile supernatural powers requiring tribute, but the group as we have it is a literary formation.
Why Tory Island specifically?
Because it looks the part and because it is genuinely remote. Toraigh lies nine miles off the Donegal coast, is frequently cut off by weather, and has an eastern promontory that is a natural fortress. An island that the mainland cannot easily reach, occupied by people the mainland does not control, is exactly where a medieval writer would place a tower holding the island's stolen children — and where nineteenth-century islanders, in turn, would site the tyrant their own folklore remembered.
Is the one-eye, one-arm, one-leg description meant literally?
Probably not originally. Irish sources describe warriors and satirists adopting a deliberate posture for hostile magic — standing on one leg, with one arm out and one eye closed — while pronouncing a curse. A being permanently in that configuration reads as permanently in the act of malediction. Later writers, working from the words rather than the practice, produced the literal amputee monsters that fantasy has inherited.