There is, though: that's exactly why we can communicate in the first place. The fact that one can have spoken language mastery without literacy also suggests we really don't need to be defining words explicitly in order to use them effectively.

Similarly, I'd speculate thay the word "blog" was likely in usage for years before it showed up in a dictionary. It would have been added to that dictionary based on its existing commonality -- so I don't see how shared written word definitions really help at all, even with new coinages.

Defining words in a meaningful way (pun intended) is actually a really difficult proposition. A lot of that comes from the fact that context means a whole lot, and words may also have different meanings to different people. It can be useful in some situations to have some written definitions -- e.g., legal proceedings, where word meanings need to be locked down to avoid possible ambiguities. Mostly this is done as a matter of convenience, though, and within a very specific domain.