Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
lagas
←
Breton
lagad
(cognate)
←
Proto-Brythonic
*llugad
(inherited)
←
Welsh
llygad
(cognate)
→
Breton
lagad
(cognate)
→
Welsh
llygad
(cognate)
→
Cornish
dewlagas
(prefix)