Why is the Croatian word "vjetar" spelt with "je" rather than "e"?

Question

Why is the Croatian word "vjetar" spelt with "je" rather than "e"? "je" comes from Proto-Slavic yat, and 'e' comes from Proto-Slavic 'en'. But there was 'en' in Proto-Slavic word for "wind", as we see by Latin "ventus" and English "wind".

Answer 1

The Proto-Slavic original word for ‘wind’ did have the yat’ (ě):

*vě̀trъ m — From Proto-Balto-Slavic *wētras, from Proto-Indo-European *h₂weh₁-. Cognate with Lithuanian vė́tra (“storm”), Latvian vētra (“storm”), Old Prussian wetro (“wind”), Latin ventus (“wind”), Sanskrit वाति (vāti, “to blow”).

Latin ventus is derived from the same PIE root h₂weh₁- with the participial suffix -nt-:

ventus m — From Proto-Italic *wentos, from Proto-Indo-European *h₂wéh₁n̥ts (“blowing”), present participle of *h₂weh₁- (“to blow”).

Answer 2

The vjetar comes from proto-Slavic větrъ, from Proto-Balto-Slavic wētras, from PIE h₂weh₁tros, so there was no "-en-" in it.

The Latin "ventus" and English "wind" come from PIE h₂wéh₁n̥ts.