Where does “-aw” come from?

-aw (Middle Welsh) comes from Proto-Brythonic -ọβ̃ — Forms verbal nouns, originally from ā-verbs.

Ancestry of “-aw”, step by step

Step	Language	Word	Meaning
1	Proto-Brythonic	-ọβ̃	Forms verbal nouns, originally from ā-verbs

-aw — Etymology, Origin & Word History | Etymology Explorer