Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Middle Welsh
-us
←
Proto-Brythonic
*-ʉs
(derived)
←
Cornish
-us
(cognate)
←
Latin
-ōsus
(derived)
→
Welsh
-us
(inherited)