From Latin 'una' meaning one, or Irish 'Oona' meaning lamb. Used in Spenser's Faerie Queene.
Una is among the oldest and most resonant names in the Irish and broader Celtic tradition, with roots that reach deep into mythology. Its most widely accepted derivation is from the Old Irish *uan* ("lamb") or alternatively from Latin *una* ("one," "unity"), and scholars have long debated which strand came first. In Irish mythological cycles, Úna appears as a fairy queen — a supernatural woman of extraordinary beauty associated with the otherworld — lending the name an otherworldly shimmer from the very beginning.
Edmund Spenser immortalized the name in English literary history through his epic allegorical poem *The Faerie Queene* (1590–1596), in which Una represents Truth and the true Protestant church — a figure of radiant purity who travels under constant threat, accompanied by a lion who recognizes her goodness instinctively. Spenser's Una became one of the most celebrated allegorical characters in English literature, and the name carries that echo of moral luminosity and singular integrity to this day. Through the nineteenth and early twentieth centuries, Una was a well-loved name among Irish families both at home and in the diaspora, carried by figures ranging from the actress Una O'Connor to the writer Una Troy.
It fell into relative quietude in the mid-twentieth century, but the broader revival of short, ancient-feeling names — Iris, Vera, Cora — has brought Una back into view. Its brevity is one of its greatest strengths: three letters, two syllables, a sound as clean and unornamented as its best allegorical meaning. One.
Whole. True.