Meaning of chicken-and-egg

chick•en-and-egg

Pronunciation: (chik'un-un-eg', -und-), [key]
— adj.
  1. of, pertaining to, or being a dilemma of which of two things came first or of which is the cause and which the effect: a chicken-and-egg question of whether matter or energy is the basis of the universe.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.