"It is noon."
Meri-dies. Originally "Medidies" (medi-dies),
(linguistically called a dissimilation)
Medi = (medius) = between, half-way.
French is the only one I know directly from Latin:
midi (from mi-dies, or directly from abbreviated Latin form "medi")
English midday (mid-day), half of the day.
Spanish mediodía (medio = half, día = day)
Italian mezzogiorno (mezzo = half, giorno = day)
Meridiem = accusative of meridies, gave French méridien, and from it, English meridian.
In French "midi" is not only a time of the day, it's also a place (to the South), in Latin, meridionalis is also a place, located to the South. It's the reason why it gave "méridien" and "meridian". And in French "méridional" = Southern.
It's the same in other Romance language, they have all a "meridional".