Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Breton
merc’h
→
Welsh
merch
(cognate)
→
Cornish
myrgh
(cognate)
→
Cornish
mergh
(cognate)