> Because there is no spacing in Chinese so there can be some ambiguity about word boundary.
Reasonable people can disagree, but I think it's safe to say that mh would be broadly considered a word by most. And anyway, languages are generally not defined by how they are written, but by how they are spoken. Indeed many languages have no formal written form (heck, in cantonese there are major grammatical words with no written form at all.)
> By the way, it is "m" for 5 in Cantonese.
It is ngh, low rising tone. I'm sure you can verify this online.