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