Interesting, it's just like the English dialectal "no but", which also means "only". "He's no but a baby."
So it's only as in "just,merely"?
I've noticed from road signs that "only" is usually translated as "yn unig". How do these two phrases differ?
Late reply - and not from a native Welsh speaker. My thought is that "yn unig" means "only" in the sense of "your sole choice", where as "dim ond" means "only" in the sense of the small end of a continuous scale, such as "only four ounces, not several pounds" or "only walking pace not motorway speed". (Posting this for confirmation of my understanding as much as to try to answer the question.)