When would you use o'r blaen as opposed to cyn? Do they mean the same thing?
Hmm, well one example would be "I have never done this before" which would be "Dwi byth wedi gwneud hyn o'r blaen" which if I wanted to use "Cyn" I would phrase as something like "Dwi byth wedi gwneud hyn cyn heddiw" (I have never done this before today). I guess it might be that you use "cyn" if you are talking about something being before something i.e "before today"="cyn heddiw", "before going to the shop"="cyn mynd i'r siop", whereas "o'r blaen" is used when not referring to something coming before something else. I can't say for certain since I've never known a rule I just go with what feels right.
o'r blaen = before (previously)
cyn = before (prior to)
Please correct me if I am wrong.