Possibly from Irish 'onna' (ash tree) or Japanese 'onna' (woman/female).
Onna is a name of layered cultural origins, each lending it a distinct color. In its most common Western reading, Onna is understood as a variant of Anna, the Latinized form of the Hebrew Hannah — from the root Channah, meaning 'grace,' 'favor,' or 'he has favored me.' Hannah appears in the Hebrew Bible as the deeply devoted mother of the prophet Samuel, and her prayer of faith became one of the most celebrated passages of scripture, casting the name permanently in associations of steadfast love and answered longing.
The streamlined Onna form strips away the doubled consonant and carries the name's essence with a clean, open sound. In Japanese, 'onna' (女) is the standard word for 'woman' and is one of the oldest characters in the written language, its form derived from a pictograph of a kneeling female figure. While it functions primarily as a common noun rather than a given name in modern Japan, this linguistic echo gives Onna an interesting cross-cultural resonance — particularly for families with Japanese heritage or an interest in Japanese culture.
The samurai class of female warriors called 'onna-bugeisha' drew on this word, and their legacy has inspired modern literature and cinema. In Dutch and Frisian traditions, Onna also appears as an independent given name with deep regional roots in the northern Netherlands and coastal areas of Germany. This Frisian Onna is a proper given name in its own right, appearing in genealogical records stretching back several centuries, lending the name genuine European historical standing quite separate from its Hebrew lineage.