Where does “decades” come from?

Decades comes from Middle French decade, from Late Latin decas, from Ancient Greek δεκάς, ultimately from Proto-Indo-European déḱm̥ meaning ten.

decades (English): plural of decade

Definitions

Step	Language	Word	Meaning
1	English	decade	A group, set, or series of ten, particularly
2	Middle English	decade	—
3	Middle French	decade	a series of 10 books
4	Latin	decās	a decade (period of ten years)
5	Ancient Greek	δεκάς	the number ten; a group of ten, decade
6	Ancient Greek	-ᾰ́ς	group of
7	Proto-Indo-European	-ónts	Derives nouns denoting body parts
8	Hungarian	önt	to pour; to cast; accusative singular of ön
9	Hungarian	ön	you
10	Hungarian	ön-	self-
11	Turkish	ön	front
12	Ottoman Turkish	اوك	voice (of human or animal); sound
13	Proto-Turkic	ǖn	sound, voice