Might be the wrong discussion to ask, but i am an American. Is this the word for the word PEN, or is this the Welsh-ized version of a "Biro"? I know it can be used in place of each other, but what if i want to talk about a Non-biro brand pen?
The problem for Welsh is that the word 'pen' means head and so it needs another word for the English pen.
There are various options, a very posh word is the 'ysgrifbin' which is the word for the fountain or cartridge pen.
Since the 'biro' brand ballpoint was the original and for a while also in English, at least in the UK, was the usual word for a ballpoint pen it was adapted into Welsh as the word for a ballpoint pen.