Another pecularity of French is the tendency to supercomposition.

Like the expression au jour d'aujourd'hui which means "the day of today", however, aujourd'hui itself mean "the day of today", because hui is the Old French word for "today" and aujourd' is obviously the concatenated form of "au jour de".

But it does not end there: the Old French word hui evolved from "hoc diem", which means "this day" in Latin.

At the end, the best explanation of au jour d'aujourd'hui is

    (the-day-of
       (the-day-of 
         (this (day)))

which is fascinating.