It happens sometimes that persons who rely almost exclusively on the CCC and the Compendium for their understanding of Catholicism mistakenly think that the terminology in those books is the norm or is the standard or is somehow required. Those works were written by several persons, with (name removed by moderator)ut from many persons, and the wording is sometimes a compromise between a number of different ways of expressing a doctrine. This results in some unevenness to the wording and to the terminology, which most persons do not notice.
Terminology is not doctrine. There are required beliefs, but not required terminology. It is also not true that the Church has one static set of terms used in theology. Terminology various across the centuries, across different documents, even within the same document.
However, some terminology is more fitting than other terminology.
Some persons prefer to use ‘grave matter’ for an act that is objectively a mortal sin, and only use the term ‘mortal sin’ for a sin that is an actual mortal sin (grave matter, full knowledge, full consent). I find this approach problematic because it does not allow you to call a gravely disordered act mortal sin unless you know that the act was done with full knowledge and full consent. In most cases, one would have no way of knowing that. The result is that objectively gravely disordered acts, such as abortion, cannot be called ‘mortal sin’. One would only be able to state that the many abortions that occur worldwide are ‘grave matter’ and that we have no way of knowing how many of these abortions are ‘mortal sin.’
I think a better approach is to use ‘mortal sin’ or ‘objective mortal sin’ for those acts that are objectively gravely disordered, and to use ‘actual mortal sin’ when all three conditions are present (grave matter, full knowledge, full consent). There are a couple of infallible teachings of the Church that use the term ‘actual mortal sin’ (Council of Florence, Benedictus Deus), which then allows the term ‘mortal sin’ or ‘objective mortal sin’ to be used for any gravely disordered act.
It is then possible to call gravely immoral acts, such as abortion, euthanasia, blasphemy, malice, lust, etc., mortal sins, without having to always add, ‘if done with full knowledge and full consent.’