You can use a quick comical definition to liven up a public speaking engagement. As always, make sure the word defined is relevant to the point you are trying to make. Here are some definitions I like:
Banker: A fellow who lends you his umbrella when the sun is shining and wants it back the minute it begins to rain. Mark Twain (similar quotation by Robert Frost).
You wouldn't use this one if you were talking to bankers, but if you are a banker talking to nonbankers you could change it thusly:
"Some people say that a banker is a person who lends you his umbrella when the sun is shining and wants it back the minute it begins to rain. That is not true. I would lend you my umbrella anytime at X percent above prime with two points. (Possible extender line) If you want to borrow MONEY, that's a different story."
City Life: Millions of people being lonely together. Henry David Thoreau
A man who just sits and thinks, mostly sits. Woodrow Wilson
A man who is too cowardly to fight and too fat to run. Elbert Hubbard
A man with two perfectly good legs who has never learned to walk. Franklin Delano Roosevelt
Death: To stop sinning suddenly. Elbert Hubbard
Jury: Twelve persons chosen to decide who has the better lawyer. Robert Frost
Radical: A man with both feet planted firmly in the air. Franklin Delano Roosevelt
Song: The licensed medium for bawling in public things too silly or sacred to be uttered in ordinary speech. Oliver Herford
Zoo: A place devised for animals to study the habits of human beings. Oliver Herford
There are literally thousands of these definitions available in comedy books, quotation books, and books for speakers. In many cases you will have several to choose from on any given topic. I probably had at least 20 choices on the subject of conservatism alone.