The first one is a very handy (and free!) Welsh-English-English-Welsh dictionary that should work on both Android (from 4.0 and up) and iOS phones (from 7.1 and up). The second one is actually a Welsh-Welsh dictionary, very thorough, too, (if, like me, you're into etymology hunting, you'll love it) and it's also free. That last one is still sadly absent on the Apple store, but it should work on Android phones (from 2.2 and up).
Here are the links if you'd like to find out more:
https://play.google.com/store/apps/details?id=com.cysgliad.android.apGeiriaduron
https://play.google.com/store/apps/details?id=dk.emp.gpc
https://apps.apple.com/us/app/ap-geiriaduron/id570171569
Enjoy!
