Where does “pentagonal” come from?

pentagonal (Portuguese) comes from Portuguese pentágono, from Late Latin pentagonum, from Ancient Greek πεντάγωνον, from Ancient Greek πεντάγωνος, from Ancient Greek γωνία, from Ancient Greek γόνυ, from Proto-Hellenic gónu, from Proto-Indo-European ǵónu — knee.

pentagonal (Portuguese): pentagonal of, relating to, or shaped like a pentagon

Definitions

pentagonal of, relating to, or shaped like a pentagon

Ancestry of “pentagonal”, step by step

Step	Language	Word	Meaning
1	Portuguese	pentágono	pentagon
2	Late Latin	pentagonum	pentaphyllon
3	Ancient Greek	πεντάγωνον	pentagon
4	Ancient Greek	πεντάγωνος	five-angled
5	Ancient Greek	γωνία	corner, angle; joiner's square; cornerstone
6	Ancient Greek	γόνυ	knee
7	Proto-Hellenic	gónu	knee
8	Proto-Indo-European	ǵónu	knee

Every word from Proto-Indo-European ǵónu →Every word from Proto-Hellenic gónu →Every word from Ancient Greek γόνυ →