Gareth King’s Modern Welsh Dictionary is great for learners - it has example phrases of spoken and written Welsh, so that you can see the language in context
via siaronjames at https://en.forum.saysomethingin.com/t/a-graduated-english-welsh-spelling-book-1857/38542/4
A Graduated English-Welsh Spelling Book by John Lewis
Some of the words may have shifted a bit since 1857, but there's something delightfully subversive about considering using this book to learn/practice Welsh in 2023.
https://duome.eu/chrisaldrich/progress
Duolingo progress with words and grammar tabs
https://www.digitalmedievalist.com/opinionated-celtic-faqs/learn-medieval-welsh/
Geiriadur Prifysgol Cymru The Really Big Welsh dictionary, the Welsh equivalent of the OED