Where does “hyrwyddwyr” come from?

hyrwyddwyr (Welsh) comes from Welsh ŵyr, from Middle Welsh wyr — Soft mutation of gwyr.

Ancestry of “hyrwyddwyr”, step by step

hyrwyddwyr traces back through two separate lines of ancestry.

via Welsh ŵyr

StepLanguageWordMeaning
1WelshŵyrSoft mutation of gŵyr; grandson, grandchild
2Middle WelshwyrSoft mutation of gwyr

via Welsh hyrwyddo

StepLanguageWordMeaning
1Welshhyrwyddoto promote to attempt to popularise, to further
Every word from Middle Welsh wyrEvery word from Welsh ŵyr