The difference between an encyclopedia and a dictionary can sometimes be difficult to pin down. After all, we tend to use them for similar purposes. However, an encyclopedia should go beyond a mere definition.
This distinction is the focus of a policy called "Wikipedia is not a dictionary". It says a Wikipedia entry is defined by the concept, not what a thing is called. A dictionary is the opposite: a single concept will have multiple entries for each word.
For example, the Wikipedia article Tornado also mentions "twisters" and "cyclones" in its first paragraph. In a dictionary each word would have its own entry, with similar definitions.
When a word doesn't represent a well-developed concept, like whatever slang the kids are using this week, the future of the Wikipedia entry about it is bleak. But worry not: Urban Dictionary has what you seek.