a. (in demonstration) the use of each of two propositions to establish the other.
b. (in definition) the use of each of two terms to define the other.
2. a situation in which effort to solve a given problem results in aggravation of the problem or the creation of a worse problem: a vicious circle where the more I give them, the more they expect.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.