Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Breton
oan
←
Proto-Brythonic
*oɨn
(inherited)
←
Proto-Celtic
*ognos
(inherited)
←
Welsh
oen
(cognate)
←
Proto-Indo-European
*h₂egʷnós
(inherited)
←
Old Irish
úan
(cognate)
→
Welsh
oen
(cognate)