I like seeing how this verb uses the reflexive "ym" to change "deol" (expulsion) into ymddeol, (retirement)!
I've only ever seen it used to mean "To stop working" and from what I get from Geiriadur Prifysgol Cymru that is the only use for it.
That's what I figured, but I have been surprised by some of the translations on other Duolingo courses.
Is the northern spelling "ymddeuol" accepted by DuoLingo? I'm not sure how official it is, but I see it a lot on Facebook in the posts from the north.
That is not a dictionary word, nor can I find it in a couple of dialect books. It does pop up a little on the web, but not apparently tied to a particular area. Probably just a mis-spelling.
There is a word deuoli, to double up, or to dual (a road). Quite easy for people to mix up their spellings of similar sounding words.
I've just come back from an Informal Welsh course in Abergavenny (SE Wales) and the spelling with 'u' was what was given for 'to retire'.
As Ibisc said "ymddeuol" is a misspelling. It's not included in the GPC which includes both modern, traditional and many regional variations. Another hint to it being a misspelling is that "Deholi/Deol", the root word of "Ymddeol" also lacks it as an alternate spelling.