Great points! I agree elaboration of the definition of a term is paramount in cases where a more specific meaning based on culture or a group is the case. But do you think asking for personal definitions at the outset of a discussion (or at any other point) invites interpretation that may completely take a different direction to the word's originally universally understood and intended meaning?
It certainly can lead to people using terms not intended by the author of a thread. However, I would say that this can actually be a positive thing when taking the spirit of exchanging information into consideration. On a religious forum, people may talk about "God" with the intention of only discussing a specific interpretation of the Christian God. That word means something different to, say, a Hindu whose input into the conversation could offer insights into a topic that the OP hadn't considered.
The flip side of this of course is that people are also free to narrow down their definitions from the outset if they wish. "I want to talk about God as understood by Jehovah's Witnesses," for example. In that case, the discussion is based on a much narrower/more specialised definition of the word "God."
Finally, there's the question of whether people should change established definitions to begin with. Honestly, sometimes you
have to. Vast as the English language may be, some ideas don't have a pre-allocated word that encapsulates the precise meaning and connotations of said idea. The choice then is to either make up your own or find a best fit. Using the example of God again, a naturalistic Pantheist would use that word to express their views on the universe because they see it as the best fit. While they're not talking about a supernatural, sentient creator, they are talking about the biggest, most powerful thing they can conceive of that they also feel incredible wonder and awe towards.