Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Breton
c'hwec'h
←
Proto-Brythonic
*hwex
(inherited)
←
Proto-Celtic
*swexs
(inherited)
←
Proto-Indo-European
*swéḱs
(inherited)
→
Breton
triwec'h
(compound)
→
Breton
c'hwezek
(compound)