Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Breton
eizh
←
Proto-Brythonic
*üiθ
(inherited)
←
Proto-Celtic
*oxtū
(inherited)
←
Proto-Indo-European
*oḱtṓw
(inherited)
→
Breton
eitek
(compound)