English. The Gaelic form is acccented: Ùna (Irish) or Úna (Scottish). The Irish Gaelic form may be Anglicized as Oona or Oonagh and the Scottish Gaelic form may be Anglicized as Euna.
The origin of the given name Una is generally agreed to be unclear but it is strongly believed that it comes from Irish [or Scottish] Gaelic, if only because there are several variant spellings in Ireland. In Irish Gaelic, úan means "lamb".
Una is not thought to originate from una, the Latin feminine for "one", and the association with Unity suggested by some is doubtful.
The FreeREG list of Gaelic equivalents gives Hanna and Winifred as equivalents of Gaelic Una. Furthermore, the Clan MacLean website suggests that Una is the Gaelic equivalent of Ann/Anna which are generally seen as closely related to Hannah. Because the association is unclear, we have classified these latter suggestions as lesser synonyms.
ONC also gives Juno and Agnes as Anglicized forms.
A correspondent [JL4] reports a case where a Catholic woman married as Winnifred [sic] thereafter uses the name Unity. Both of these names are known to be synonomous with Una in some communities - though not all - which suggests that the cross connection between Unity, Una/Oona and Winifred might be stronger than we have assumed though it might be confined to Catholic families.