vernus.

Ultimately derived from Proto-Indo-European *wósr̥ (“spring”) (also reconstructed alternatively as *wésr̥ or *wḗsr̥), the root of Latin vēr (“spring”). The details of the derivation differ between sources. Possibly the reflex of a deadverbial adjective in *-no- built on a locative form of the Proto-Indo-European *wósr̥ /*wésr̥ /*wḗsr̥ noun. According to one hypothesis, *vērno- developed from syncope of *-i- in a pre-form *vēri-no-, built on a reconstructed locative singular case-form *vēri (compare the leveled stem vēr- seen in inflected forms of the Latin noun vēr). Gąsiorowski 2012 instead proposes the following derivation from the PIE locative stem *wesri, where the final Latin form vernus results from haplology or syncope of *er: *wesri-no- → *wezr̥₂no- → *wererno- → vernus. As an alternative to derivation from a locative form, De Vaan suggests that the word could come from *wesinos (with rhotacism of *s and syncope of *i). By surface analysis, vēr + -nus.