What does the welsh word saes mean?

"Sais" is an Englishman, and "Saeson" the English people.

"Saesnes" is an English woman, and "Saesneg" the English language.

It is basically the Welsh for "Saxon". The English Word "English" comes from "Angle", and the Angles and Saxons (Anglo-Saxons, collectively) occupied much of what is now England when they invaded Britain in the early 5th century AD.