Cas"u*ist*ry (?), a. 1. The science or doctrine of dealing with cases of conscience, of resolving questions of right or wrong in conduct, or determining the lawfulness or unlawfulness of what a man may do by rules and principles drawn from the Scriptures, from the laws of society or the church, or from equity and natural reason; the application of general moral rules to particular cases.

The consideration of these nice and puzzling question in the science of ethics has given rise, in modern times, to a particular department of it, distinguished by the title of casuistry.
Stewart.

Casuistry in the science of cases (i.e., oblique deflections from the general rule).
De Quincey.

2. Sophistical, equivocal, or false reasoning or teaching in regard to duties, obligations, and morals.

• the process of answering moral or ethical questions via interpretation of rules of ethics or cases that illustrate such rules
  
• rationalization, that is, a bogus argument designed to defend an action or feeling