Definition of "proclivity"

This therefore was the reason why the still comparatively young though dissolute man who now addressed Stephen was spoken of by some with facetious proclivities as Lord John Corley.

1922 February, James Joyce, Ulysses, Paris: Shakespeare and Company, […]

The idea is that the choice of x {\displaystyle x} when facing the alternatives { x , y } {\displaystyle \{x,y\}} reveals a proclivity for choosing x {\displaystyle x} over y {\displaystyle y} that we should expect to see reflected in the individual's behavior when faced with the alternatives { x , y , z } {\displaystyle \{x,y,z\}} .

1995, Andreu Mas-Colell, Michael D. Whinston, and Jerry R. Green, Microeconomic Theory, Oxford University Press, page 10