Examples:
cartography
card
archaeology
archetype
monarchy
legal
loyal
purse
personal
cinema
kinase
car
carpenter
hippopotamus
Mesopotamia
dative
data
date
...
Middle English
oo
←
Old English
ān
(inherited)
←
Ancient Greek
ὦ
(cognate)
→
English
oh
(mention)
→
English
oh
(mention)
→
English
-o
(mention)