Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
-yas
→
Welsh
-iad
(cognate)
→
Cornish
broweghyas
(compound)
→
Cornish
broweghyades
(compound)