It is worth stopping and asking how one might define certain things should one be required to do so. It helps clarify one's understanding of the world. This is particularly worthwhile when it comes to familiar things - objects as well as concepts. There are many things with which we are so familiar that trying to give a clear and succinct definition or description can prove very difficult. Some things may even prove impossible to define satisfactorily. Dictionaries may give an idea of how words are used but what about the real essence of a thing?
Here are two definions that won't be found in any dictionary:
What is a philosopher?
"Everything is perceptually modified by proximity and perspective and philosophy is the capacity to pan in and out at will - and a philosopher is someone who can do this."
Christopher J. Ross - Tunnel Visions: Journeys of an Underground Philosopher (6) p12.
Similarly, What is a gentleman?
"A gentleman is a man who can describe a woman without using his hands."
Unattributed (and perhaps rightly so)