Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
kledh
←
Proto-Brythonic
*kleð
(inherited)
←
Welsh
gogledd
(cognate)
→
Cornish
kledhbarth
(compound)
→
Cornish
a-gledh
(compound)