Polydeuces, better known to many by his Roman name of Pollux, was the twin brother of Castor. His name appears to mean 'much sweetness', from polys, 'much' and deucos, 'sweet'. The latter word was a variant of gleucos, which meant 'sweet new wine' (what the Romans called mustum, in English, 'must').

The concept as a whole could relate to some religious or other festival when much new wine was drunk. However, in considering the name of Castor we mentioned an interpretation 'light' for him. If we then see him as representing the day in some way, it seems logical that Polydeuces, his twin, could symbolise the night.

To get such a sense, we can derive the latter half of Polydeuces' name not from deucos but from deuo, 'to wet', 'soak', this referring to the dew of the night. (This is perhaps not to go quite so far as the nineteenth-century German philologist Friedrich Welcker, who made Castor the same as 'Aster', 'star', and Polydeuces the same as 'Polyleuces', 'much light', in other words Castor was the sun and Polydeuces the moon!)