Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Gaulish
con-
←
Breton
kev-
(cognate)
←
Breton
kem-
(mention)
←
Proto-Celtic
*kom-
(inherited)
←
Welsh
cyf-
(cognate)
←
Proto-Indo-European
*ḱóm
(derived)
←
Old Irish
com-
(cognate)