Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
dillas
←
Breton
dilhad
(cognate)
←
Proto-Celtic
*dī-
(derived)
←
Welsh
dillad
(cognate)
→
Breton
dilhad
(cognate)
→
Welsh
dillad
(cognate)