Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Breton
Merc'her
←
Welsh
Mercher
(cognate)
←
Cornish
de Merher
(cognate)
←
Latin
Mercurius
(borrowed)
→
Welsh
Mercher
(cognate)