For-mu-la, ffurfreol, ffurf
For-ti-fy, cadarnhau; caeru, cryfhau
For-tu-nate, ffyniannus, ffodiog
Foun-da-tion, sail, sylfaen
Fran-gi-ble, hydor, breuol
Fra-ter-nal, brawdol, brawdgar
Frat-ri-cide, brawdladdiad
Fraud-u-lence, dichellgar, twyllgarwch
Fraud-u-lent, twyllodrus
Friv-o-lous, dibwys, disylwedd