'Una' originates from Irish, specifically the word 'Úna', where 'uán' meant 'lamb'; it has also sometimes been associated with Latin 'unus' meaning 'one'.

'Una' changed from Old Irish 'Úan' (or 'Úna') and eventually became the modern English name 'Una'; influence from Latin 'unus' occurred later through contact and folk etymology.

Initially it meant 'lamb' (from Old Irish), but over time it evolved into a personal name whose sense is mainly identifying a person and is sometimes associated with the idea of 'one' or 'unity'.