sopio.

From Proto-Indo-European *swep- (“to sleep”). However, the specifics of the etymology are disputed: * According to the LIV, from Proto-Indo-European *swṓp-ye-ti, whence also perhaps Old Norse sǿfa (“to kill”). However, according to De Vaan, the existence of such a verbal class in PIE is uncertain. * Nussbaum proposed that the term may have emerged as a denominative to a root noun *swṓp-s, which is itself possibly—according to Nussbaum—the source of the thematic nouns *swépnos (“sleep, slumber”) and *supnós (“sleep”). However, according to Vine, there is no evidence to more directly support the existence of such a root noun and PIE n-stems, including the aforementioned examples, are otherwise attributed to original r/n stems, rather than root nouns. * Alternatively, Vine reconstructs a PIE present of the shape *swṓp-eye-ti, which developed into *swṓp-ije-ti according to a rule whereby unstressed *e prior to *j was reduced to *i. This pre-form would then evolve into the attested present sōpiō.

Nikolaev connects the word to prosapia (“race, lineage”), and derives both from Proto-Indo-European *seh₂p- "strike", with semantic development "strike > have sexual intercourse > beget".