Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Welsh
agos
←
Proto-Celtic
*onkus
(inherited)
←
Welsh
ad-
(mention)
←
Old Irish
ocus
(cognate)
→
Welsh
agosáu
(affix)
→
Irish
agús
(cognate)