Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Old Irish
cethramad
←
Proto-Celtic
*kʷetwariyos
(derived)
←
Old Irish
-mad
(affix)
→
Irish
ceathrú
(inherited)
→
Scottish Gaelic
ceathramh
(inherited)
→
Manx
kerroo
(inherited)