What is "plurisecular"? Can't find this word's meaning, only translations

In short, it means centuries-old or age-old.

It's formed from the prefix pluri and the word secular.

Both from Merriam-Webster.

pluri-:

: many : having or being more than one : MULTI-
// pluriaxial [having more than one axis]
// plurilocular [divided into chambers]

secular:

3 a : occurring once in an age or a century
3 b : existing or continuing through ages or centuries
3 c : of or relating to a long term of indefinite duration
        // secular inflation

Secular has other senses, mostly related to things that are of the material world, or not religious, but in the sense used for this combined word it's this one.

From a translation by Linguee between Spanish and English (emphasis mine):

[...] le competen las tareas y los honores que por antigua tradición y Estatuto se reconocen a esta plurisecular magistratura.

[...] and is vested with the rights and honours to which this centuries-old magistracy is entitled to by tradition and under the Charter.