There are several Welsh-English dictionaries and rhyming dictionaries available online &/or as apps now, and I thought it’d be useful to list them. All of the Welsh/English dictionaries go in both directions. The Welsh rhyming dictionaries are life-savers in playing with Welsh poetry.
Welsh / English Dictionaries
Free, online, no separate mobile app. Great advantage is being able to search by part of a word or phrase, the beginning of a word, or the end of a word – so, if you’ve heard ‘yn lân’ on the radio and don’t know if the underlying word that would make sense is lân or glân, you can figure it out. Because it includes phrases, can be helpful in understanding idioms. Offered by University of Wales Trinity Saint David.
2. Ap Geiriaduron
Free, mobile app for iTunes or Android (downloadable in the appropriate app stores). Bigger collection of words than www.geiriadur.net, because it includes entries from more specialized dictionaries like Y Termiadur. Offered by Bangor University.
Free (but requires registration), online, no mobile app. I only found this recently but am impressed so far. Many definitions include example sentences, and (fantastic!) in the entry for every verb there’s a button marked rhediad/conjugation that leads to the full conjugation in both colloquial and literary styles. It’s also a Welsh/Welsh and English/English dictionary; every Welsh word is defined in Welsh before the corresponding English word is given. Many entries also have a sound clip pronouncing the word, and many list synonyms in Welsh. Created (?) by D. Geraint Lewis, who’s written thesauruses and materials for learners.
4. www.geiradur.co.uk --> Geiriol
5 gpb (payable through Paypal), downloadable app, available only for Windows (Windows XP SP3, Vista, 7, 8, 8.1). I haven’t bought it, but I have bought Odlau from the same people (see below). Created by Malcolm Weindling.
Welsh Rhyming Dictionaries
1. www.geiriadur.co.uk --> Odlau
5 gpb (payable through Paypal), downloadable app, available only for Windows (Windows XP SP3, Vista, 7, 8, 8.1). Extremely flexible searchable Welsh rhyming dictionary and more You can pull up, for instance, all one-syllable world staring in br-, or all words that include an internal syllable starting in N and ending in D – the kinds of searches useful in writing cynghanedd verse. I found and bought this yesterday and have high hopes for it. Created by Malcolm Weindling.
2. Yr Odliadur
Free, online, no mobile app. Standard rhyming dictionary listing Welsh word endings (for instance, -en will pull up all the Welsh words that are considered to rhyme with other Welsh words ending in -en, appropriately accounting for vowel combinations; -en would give you angen and heulwen but not maen or oen. Created by Geraint Jones at Wolfson College, Oxford.