Examples: cartography card archaeology archetype monarchy legal loyal purse personal cinema kinase car carpenter hippopotamus Mesopotamia dative data date
...
Proto-Celtic *an-

→ Welsh an- (inherited)
→ Welsh af- (mention)
→ Welsh amrwd (derived)
→ French auvent (derived)
→ Irish an- (inherited)
→ Irish an- (inherited)
→ Irish éa- (inherited)
→ Old Irish an- (inherited)
→ Old Irish é- (inherited)
→ Middle Welsh an- (inherited)