Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
caugh
←
Proto-Brythonic
*kax
(inherited)
←
Proto-Celtic
*kakkos
(inherited)
←
Proto-Celtic
*kakkā
(mention)
→
English
caca
(cognate)