caligo.

Formation from an earlier adjective is possible, similarly to several similar nouns in -īgō, examples at rōbīgō, with the verb deriving from the noun, as cālīgō (noun) + -ō. A possible reading in Pacuvius suggests earlier verb semantics as “to make dark”, consistent with this construction. Possibly from Proto-Indo-European *kel- (“dark spot”), suggested to be connected to columba (“dove, pigeon”), Sanskrit कलङ्क (kalaṅka, “dark blemish”), Serbo-Croatian kâl / ка̑л ("mud, dirt"). Various further Indo-European cognates have been suggested, such as Ancient Greek κελαινός (kelainós, “dark, black”), Ancient Greek κηλίς (kēlís, “spot, stain”) and the rare adjective Latin cā̆lidus (“having a white spot on the forehead”).

Formation from an earlier adjective is possible, similarly to several similar nouns in -īgō, examples at rōbīgō, with the verb deriving from the noun, as cālīgō (noun) + -ō. A possible reading in Pacuvius suggests earlier verb semantics as “to make dark”, consistent with this construction. Possibly from Proto-Indo-European *kel- (“dark spot”), suggested to be connected to columba (“dove, pigeon”), Sanskrit कलङ्क (kalaṅka, “dark blemish”), Serbo-Croatian kâl / ка̑л ("mud, dirt"). Various further Indo-European cognates have been suggested, such as Ancient Greek κελαινός (kelainós, “dark, black”), Ancient Greek κηλίς (kēlís, “spot, stain”) and the rare adjective Latin cā̆lidus (“having a white spot on the forehead”).