Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Middle Irish
secht
←
Proto-Celtic
*sextam
(inherited)
←
Proto-Indo-European
*septḿ̥
(inherited)
←
Old Irish
secht
(inherited)
→
Middle Irish
sechtmad
(affix)