Beginners' Welsh Reading Dictionary Common Welsh Words with Mutated and Other Forms, Especially for Learners and Non-Welsh Speakers Lewis, D. Geraint Heftet / 2023 / Engelsk
How Do You Say...? - A checklist of Welsh phrases, expressions, exclamations and sayings A checklist of Welsh phrases, expressions, exclamations and sayings Lewis, D. Geraint Heftet / 2025 / Engelsk
Y Diarhebion - Casgliad o Ddiarhebion Cyfoes / A Compendium of Contemporary Welsh Proverbs Casgliad o Ddiarhebion Cyfoes Cymraeg / A Compendium of Contemporary Welsh Proverbs Lewis, D. Geraint Heftet / 2022 / Engelsk
Adferfau - Disentangling the Welsh adverb Disentangling the Welsh adverb Lewis, D. Geraint Heftet / 2025 / Engelsk
Amhosib - Ffeithiau a Syniadau Fydd yn Newid dy Fywyd am Byth Ffeithiau a Syniadau Fydd yn Newid dy Fywyd am Byth Lewis, D. Geraint Heftet / 2018 / Walisisk
Geiriau Lletchwith, Y - A Check-List of Irregular Word Forms and Spelling Lewis, D. Geraint Heftet / 2009 / Walisisk
Treigladur, Y - A Check-List of Welsh Mutations (Argraffiad Newydd) Lewis, D. Geraint Heftet / 2018 / Walisisk
Llyfr Enwau, Y - Enwau'r Wlad / Check-List of Welsh Place-Names, A A Check-List of Welsh Placenames Lewis, D. Geraint Heftet / 2007 / Engelsk
Ar Flaen fy Nhafod - Casgliad o Ymadroddion Cymraeg Casgliad o Ymadroddion Cymraeg Lewis, D. Geraint Heftet / 2016 / Walisisk
Arddodiaid, Yr A Comprehesive Collection of Welsh Prepositions Lewis, D. Geraint Heftet / 2021 / Walisisk
Ansoddeiriau, Yr - A Comprehensive Collection of Welsh Adjectives A Comprehensive Collection of Welsh Adjectives Lewis, D. Geraint Heftet / 2021 / Walisisk
Oriel y Bardd - Dyfyniadau Doeth a Difyr o Waith y Beirdd Dyfyniadau Doeth a Difyr o Waith y Beirdd Barddas, Cyhoeddiadau Heftet / 2023 / Walisisk
