The verb piau/biau specifically means 'owns'. It is a very irregular verb, nowadays only used in a particular pattern - it is preceded by the owner, and followed by the thing owned. (The sy is often used in the colloquial language, but it is not really needed):
- Fi (sy) biau'r car - 'I own the car' (or 'it's me who owns the car' if you want to be more emphatic in the English)
- Megan (sy) biau'r gath - 'Megan owns the cat' or 'It is Megan who owns the cat'
To say 'It's Megan's cat' we would say, perhaps, Cath Megan yw hi.