The following is an answer and/or comment by inhahe aka ColorStorm (inhahe.com - myriachromat.wordpress.com).
If you can�t define a word precisely, clearly, and quickly, that�s proof you don�t understand what you�re talking about as well as you might. (quoted from the Net). Agree? Good. Disagree? Ho-hum.

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No, I don't really agree, first, we can have a good, accurate mental conception of what a word means without necessarily being able to readily define it, if defining words isn't our forte. The meaning of a word is not its definition; definitions are ad hoc and the ability to define is a talent.

Second, not all words have a meaning that is precise or clear. The meaning of a word is determined by its popular usage, so it's really, often, a kind of indistinct blob of possible meanings, and sometimes we just have to use the best word at our disposal.

I guess you could say a person could define the word *as they meant it* in the given context, but that requires that suitable words exist in order to accurately break down the given word into other words, as to some degree all words are atomic... if you tried to recursively define every word in terms of other words, what would be at the bottom? there's no possible bottom, you must end up with either circularities or undefined words, so some of the meaning of a word is not in its other words / its definition, so you can't always necessarily adequately define a word. And even if there is a way of defining a word, again it requires that the person happen to have a talent for defining words. We don't really think in words so meanings aren't composed of words.

Also in certain contexts (such as describing popular opinions or psychosocial phenomena) it may make sense to use a word as a symbol referring to all the myriad meanings people intend when they use the word, with all their varying connotations and precepts.. and exhaustively going through all those possibilities to define the word would be impractical, and the person wouldn't know all of the possibilities anyway even though they have a kind of nebulous apprehension of the overall scape of it.

This nebulousness wouldn't be a weakness in understanding, it would be a strength, because it entails complexity in understanding and breadth of perception, just a little too complex or broad to fully assimilate as an analytical structure--in other words, to fit it into a purely structural/analytical/formal mentality would require limiting the concept to a much cruder and less advanced form. So it's not 'understanding not as well as they might' because they're understanding as well as any human mind can be expected to, just as an admixture of the structural and the nebulous--structural to the degree that it's necessary to be sensible or to be coveyed to others and to the degree that one can keep track of specifics in texture/ differentiation, but intimately tied into the nebulous as an extra, outer layer.

Another context in which it may make sense to use a word in this way is the mystical/metaphysical, as some kinds of truths are determined by collective thought anyway.