Full Idea
In the objectionable kind of infinite regress, some propositions join to constitute the meaning of some proposition, but one of them is similarly compounded, and so ad infinitum. This comes from circular definitions, where the term defined reappears.
Gist of Idea
Infinite regresses have propositions made of propositions etc, with the key term reappearing
Source
Bertrand Russell (The Principles of Mathematics [1903], §329)
Book Reference
Russell,Bertrand: 'Principles of Mathematics' [Routledge 1992], p.348