Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Cornish
glas
←
Proto-Brythonic
*glas
(inherited)
←
Proto-Celtic
*glastos
(inherited)
←
Proto-Indo-European
*ǵʰelh₃-
(root)
→
Welsh
glas
(cognate)
→
Cornish
glasrudh
(compound)
→
Cornish
rudhlas
(compound)