Where does “ymerodraethau” come from?

ymerodraethau (Welsh) comes from Welsh hemisffer, from English hemisphere, from Latin hēmisphaerium, from Ancient Greek ἡμισφαίριον, from Ancient Greek σφαῖρα, from Ancient Greek -ειδής, from Ancient Greek -ής, from Proto-Indo-European -ēs — Creates action nouns or result nouns from verbs;...

Ancestry of “ymerodraethau”, step by step

Step	Language	Word	Meaning
1	Welsh	hemisffer	hemisphere
2	English	hemisphere	Half of the celestial sphere, as divided by...
3	Latin	hēmisphaerium	hemisphere
4	Ancient Greek	ἡμισφαίριον	hemisphere
5	Ancient Greek	σφαῖρα	ball, globe, sphere
6	Ancient Greek	-ειδής	like, connected to, from the nature of, full of;...
7	Ancient Greek	-ής	adjective suffix
8	Proto-Indo-European	-ēs	Primarily forms adjectival bahuvrīhi compounds
9	Proto-Indo-European	-ess	—
10	Proto-Indo-European	-os	Creates action nouns or result nouns from verbs;...

Every word from Proto-Indo-European -os →Every word from Ancient Greek -ειδής →Every word from Ancient Greek σφαῖρα →