This is where I learned such things as that there are no "k"s in written Welsh because there wouldn't have been enough of them in a typical set of "moveable type" used for English and what dipthongs and tripthongs are.
This is a well written and useful dictionary that includes a bit of history about the Welsh language as well as guidance on pronunciation, abbreviations and personal and place names.
I was gifted this by my Welsh grandmother. It is a straightforward and clear dictionary, a pleasant size to use, clear type, and uncomplicated (unlike to Welsh language ...). Recommended, even though the word-set is now out of date.