Work on Geiriadur Prifysgol Cymru (the standard historical Welsh dictionary), for instance, started in 1921, and is by now the basis for all other work on Welsh words and terms.
Dechreuodd y gwaith ar Eiriadur Prifysgol Cymru, er enghraifft, ym 1921, ac mae wedi datblygu i fod yn sylfaen ar gyfer yr holl waith arall ar eiriau a thermau yng Nghymru.