Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Irish
gach
←
Proto-Celtic
*kʷākʷos
(inherited)
←
Welsh
pob
(cognate)
←
Middle Irish
gach
(inherited)
←
Old Irish
cach
(inherited)
←
Old Irish
cách
(mention)
→
Irish
ós
(mention)