"Το άπειρο."

Translation: The infinity.

[NicMdE21]

The great Greek philosopher Anaximander (Ἀναξίμανδρος, 610 π.Χ. - 546 π.Χ.) used "το άπειρον" as a term to refer to the basic substance that produces and absorbs all the opposites. In his view "το άπειρον" means "the indefinite" or "the infinite" or "the unlimited". (June 19, 2018)

[Walt1965]

In English ´infinity´ does not usually take the definite article; but you can say ´the infinite´, which would be a good translation here.

[AniruddhaJ20]

How is this word "άπειρο" derived?

[YPSILONZ]

I think it's α (without) + πέρας (end)

[D_..]

YPSILONZ's answer is correct. I will only add that Wiktionary often offers information on etymology. This - see Etymology 2 - was linked to the article for άπειρο.