Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Breton
arc'hant
←
Proto-Brythonic
*arɣant
(inherited)
←
Proto-Celtic
*argantom
(inherited)
←
Proto-Indo-European
*h₂erg-
(derived)
←
Old Breton
argant
(inherited)
→
Breton
arc'hanti
(compound)
→
Welsh
arian
(cognate)