Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Proto-Slavic
*o(b)-
→
English
oblast
(mention)
→
Russian
обычный
(mention)
→
Russian
обычный
(mention)
→
Slovene
o-
(inherited)