Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Scottish Gaelic
amaideachd
←
Irish
amaideacht
(cognate)
←
Middle Irish
amaidecht
(inherited)
→
Irish
amaideacht
(cognate)
→
Scottish Gaelic
amaideach
(back-formation)