Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
mergh
←
Breton
merc’h
(cognate)
←
Proto-Celtic
*merkā
(inherited)
←
Welsh
merch
(cognate)
←
Cornish
myrgh
(link)
→
Breton
merc'h
(cognate)
→
Welsh
merch
(mention)