Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
-yon
←
Breton
-ien
(cognate)
←
Proto-Brythonic
*-onos
(inherited)
←
Proto-Brythonic
*-onā
(mention)
←
Welsh
-ion
(cognate)
→
Breton
-ien
(cognate)
→
Welsh
-ion
(cognate)
→
Cornish
yonkoryon
(suffix)