Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Old Church Slavonic
нъ
←
Proto-Balto-Slavic
*nu
(inherited)
←
Proto-Indo-European
*nu
(inherited)
←
Proto-Slavic
*nъ
(inherited)