GPC is the only standard historical dictionary of the Welsh language.
It is broadly comparable in method and scope to the Oxford English Dictionary.
It presents the vocabulary of the Welsh language from the earliest Old Welsh texts, through the abundant literature of the Medieval and Modern periods, to the huge expansion in vocabulary resulting from the wider use of Welsh in all aspects of life in the last half century.
This vocabulary is defined in Welsh, and English equivalents are also given. Detailed attention is given to variant forms, collocations, and etymology.
The work is based on an ever-expanding collection of over two million citation slips gathered from a range of texts over many years.