| Singular | Plural | |
|---|---|---|
| Nominativ | obsonium, opsonium | obsonia, opsonia, obsoniaque |
| Genitiv | obsoni, obsonii | obsoniorum, obsonium, opsonium |
| Dativ | obsonio | opsoniis, obsoniis |
| Akkusativ | obsonium, opsonium | obsonia, opsonia, obsoniaque |
| Ablativ | obsonio | opsoniis, obsoniis |
| Vokativ | obsonium, opsonium | obsonia, opsonia, obsoniaque |