As an instance of the limits of replacing words with their definitions to clarify debates, this looks like an important conversation.
The fuzziest starting point for "consciousness" is "something similar to what I experience when I consider my own mind". But this doesn't help much. Someone can still claim "So rocks probably have consciousness!", and another can respond "Certainly not, but brains grown in labs likely do!". Arguing from physical similarity, etc. just relies on the other person sharing your intuitions.
For some concepts, we disagree on definitions because we don't know actually know what those concepts refer to (this doesn't include concepts like "art", etc.). I'm not sure what the best way to talk about whether an entity possesses such a concept is. Are there existing articles/discussions about that?
If I don't know what I'm referring to when I say "consciousness," it seems reasonable to conclude that I ought not use the term.
This seems significant:
http://www.theguardian.com/science/2015/aug/18/first-almost-fully-formed-human-brain-grown-in-lab-researchers-claim