Latin for 'the only codex'. The expression is used for a codex which is the only extant one bearing the text in question. In this case no actual recensio leading to a stemma is required, but emendatio of its errors is likely to become more difficult than in the case of having recourse to several manuscripts. The codex unicus may, indeed, be very far removed from the original.
In other languages
The Latin term is used throughout.