vicious circle

1. A situation in which the apparent solution of one problem in a chain of circumstances creates a new problem and increases the difficulty of solving the original problem. Also called vicious cycle.
2. A condition in which a disorder or disease gives rise to another that subsequently affects the first.
3. Logic. A fallacy in reasoning in which the premise is used to prove the conclusion, and the conclusion used to prove the premise.

[Translation of New Latin circulus vitiōsus, circular argument : Medieval Latin circulus, circular argument + Latin vitiōsus, flawed, faulty.]

A series of events in which each problem creates another and worsens the original one. For example, The fatter I get, the unhappier I am, so I eat to cheer myself up, which makes me fatter yet--it's a vicious circle. This expression comes from the French cercle vicieux, which in philosophy means "a circular proof"--that is, the proof of one statement depends on a second statement, whose proof in turn depends on the first. One writer suggests that the English meaning of "vicious" helped the expression acquire its more pejorative present sense, used since 1839.

Circle, vicious A definition is viciously circular when the term to be defined reappears in the definition, or where the notion that is being defined is implicitly contained in the definition. The definition ‘“x is good” means that we think that x is good’ is an example of the former. The definition ‘“x is good” means that ideal people like x’ is an example of the latter, since although the word ‘good’ does not recur, it seems hidden in the notion of an ideal (= maximally good) person. Reasoning is condemned as viciously circular when the conclusion is improperly concealed in the premises, or is improperly needed to get the conclusion itself from the premises (see also begging the question). It is extremely hard to say when such concealment is vicious, since there is one sense in which in any valid argument the conclusion is concealed in the premises. Controversial cases of circular reasoning in philosophy include Descartes's alleged appeal to God to certify that the clear and distinct ideas that enabled him to prove the existence of God did not deceive him, and the use of the fact that induction has worked well in the past as an argument for supposing that it will work well in the future. For Russell's particular use of the concept, see vicious circle principle.

A condition in which a disorder or disease gives rise to another that subsequently affects the first.

The noun has 2 meanings:

Meaning #1: one trouble leads to another that aggravates the first
  Synonym: vicious cycle

Meaning #2: an argument that assumes that which is to be proved