Where does “τριγωνομετρία” come from?

τριγωνομετρία (Ancient Greek) comes from Ancient Greek τρίγωνον, from Ancient Greek τρίγωνος, from Ancient Greek γωνία, from Ancient Greek γόνυ, from Proto-Hellenic gónu, from Proto-Indo-European ǵónu — knee.

Ancestry of “τριγωνομετρία”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	τρίγωνον	triangle; one of the Athenian lawcourts; the...
2	Ancient Greek	τρίγωνος	three-cornered; three-sided
3	Ancient Greek	γωνία	corner, angle; joiner's square; cornerstone
4	Ancient Greek	γόνυ	knee
5	Proto-Hellenic	gónu	knee
6	Proto-Indo-European	ǵónu	knee

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