Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Proto-Celtic
*axtā
→
Welsh
-iaeth
(inherited)
→
Welsh
-aeth
(inherited)
→
Cornish
-ieth
(inherited)
→
Old Irish
-acht
(inherited)